Cleanup Agent docs (#22510) (#22559)

* Remove unnecessary anchor

* Remove enroll widget that's no longer used

* Break dynamic input config docs into several files

* Make sure standalone content is moved over

* Indicate that systemd is required on Linux

* Update note to reflect cloud UI change

* Fix enrollment command on deb/rpm

* Correct uninstall docs

* Commenting out upgrade command because it's not supported in 7.10

* Add upgrade CLI content back in

* Fix upgrade content to show fleet steps

* Add upgrade image

x-pack/elastic-agent/docs/elastic-agent-command-line.asciidoc

@@ -185,7 +185,8 @@ elastic-agent inspect output --output default --program filebeat
 
 Install {agent} permanently on the system and manage it by using the system's
 service manager. The agent will start automatically after installation is
-complete.
+complete. On Linux, this command requires a system and service manager like
+systemd.
 
 You must run this command as the root user (or Administrator on Windows)
 to write files to the correct locations. This command overwrites the

x-pack/elastic-agent/docs/elastic-agent-conditions.asciidoc

@@ -0,0 +1,101 @@
+[[conditions]]
+== Conditions
+
+A condition is a boolean expression that you can specify in your agent policy
+to control whether a configuration is applied to the running {agent}. You can
+set a condition on inputs, streams, or even processors. 
+
+In this example, the input is applied if the host platform is Linux:
+
+[source,yaml]
+----
+inputs:
+  - type: logfile
+    streams:
+      - paths:
+         - /var/log/syslog
+    condition: ${host.platform} == 'linux'
+----
+
+In this example, the stream is applied if the host platform is not Windows:
+
+[source,yaml]
+----
+inputs:
+  - type: system/metrics
+    streams:
+      - metricset: load
+        data_stream.dataset: system.cpu
+        condition: ${host.platform} != 'windows'
+----
+
+In this example, the processor is applied if the host platform is not Windows:
+
+[source,yaml]
+----
+inputs:
+  - type: system/metrics
+    streams:
+      - metricset: load
+        data_stream.dataset: system.cpu
+    processors:
+      - add_fields:
+          fields:
+            platform: ${host.platform}
+          to: host
+        condition: ${host.platform} != 'windows'
+----
+
+[[condition-syntax]]
+=== Condition syntax
+
+The conditions supported by {agent} are based on {ref}/eql-syntax.html[EQL]'s
+boolean syntax, but add support for variables from providers and functions to
+manipulate the values. 
+
+**Supported operators:**
+
+* Full PEMDAS math support for `+ - * / %`.
+* Relational operators `< <= >= > == !=`
+* Logical operators `and` and `or`
+
+
+**Functions:**
+
+* Array functions <<arrayContains-function,`arrayContains`>>
+* Dict functions <<hasKey-function,`hasKey`>> (not in EQL)
+* Length functions <<length-function,`length`>>
+* Math functions <<add-function,`add`>>, <<subtract-function,`subtract`>>,
+<<multiply-function,`multiply`>>, <<divide-function,`divide`>>, <<modulo-function,`modulo`>>
+* String functions <<concat-function,`concat`>>, <<endsWith-function,`endsWith`>>,
+<<indexOf-function,`indexOf`>>, <<match-function,`match`>>, <<number-function,`number`>>,
+<<startsWith-function,`startsWith`>>, <<string-function,`string`>>,
+<<stringContains-function,`stringContains`>>
+
+**Types:**
+
+* Booleans `true` and `false`
+
+[[condition-examples]]
+=== Condition examples
+
+Run only when a specific label is included.
+
+[source,eql]
+----
+arrayContains(${docker.labels}, 'monitor')
+----
+
+Skip on Linux platform or macOS.
+
+[source,eql]
+----
+${host.platform} != "linux" and ${host.platform} != "darwin"
+----
+
+Run only for specific labels.
+
+[source,eql]
+----
+arrayContains(${docker.labels}, 'monitor') or arrayContains(${docker.label}, 'production')
+----

x-pack/elastic-agent/docs/elastic-agent-debug-input-configs.asciidoc

@@ -0,0 +1,139 @@
+[[debug-configs]]
+== Debugging 
+
+To debug configurations that include variable substitution and conditions, use 
+the `inspect` command. This command shows the configuration that's generated
+after variables are replaced and conditions are applied.
+
+First run the {agent}. For this example, we'll use the following agent policy:
+
+
+[source,yaml]
+----
+outputs:
+  default:
+    type: elasticsearch
+    hosts: [127.0.0.1:9200]
+    username: elastic
+    password: changeme
+
+providers:
+  local_dynamic:
+    items:
+      - vars:
+          key: value1
+        processors:
+          - add_fields:
+              fields:
+                custom: match1
+              target: dynamic
+      - vars:
+          key: value2
+        processors:
+          - add_fields:
+              fields:
+                custom: match2
+              target: dynamic
+      - vars:
+          key: value3
+        processors:
+          - add_fields:
+              fields:
+                custom: match3
+              target: dynamic
+
+inputs:
+  - type: logfile
+    enabled: true
+    streams:
+      - paths:
+          - /var/log/{{local_dynamic.key}}
+----
+
+Then run `elastic-agent inspect` to see the generated configuration. For
+example:
+
+[source,shell]
+----
+$ ./elastic-agent inspect output -o default
+[default] filebeat:
+filebeat:
+  inputs:
+  - index: logs-generic-default
+    paths:
+    - /var/log/value1
+    processors:
+    - add_fields:
+        fields:
+          custom: match1
+        target: dynamic
+    - add_fields:
+        fields:
+          dataset: generic
+          namespace: default
+          type: logs
+        target: data_stream
+    - add_fields:
+        fields:
+          dataset: generic
+        target: event
+    type: log
+  - index: logs-generic-default
+    paths:
+    - /var/log/value2
+    processors:
+    - add_fields:
+        fields:
+          custom: match2
+        target: dynamic
+    - add_fields:
+        fields:
+          dataset: generic
+          namespace: default
+          type: logs
+        target: data_stream
+    - add_fields:
+        fields:
+          dataset: generic
+        target: event
+    type: log
+  - index: logs-generic-default
+    paths:
+    - /var/log/value3
+    processors:
+    - add_fields:
+        fields:
+          custom: match3
+        target: dynamic
+    - add_fields:
+        fields:
+          dataset: generic
+          namespace: default
+          type: logs
+        target: data_stream
+    - add_fields:
+        fields:
+          dataset: generic
+        target: event
+    type: log
+output:
+  elasticsearch:
+    hosts:
+    - 127.0.0.1:9200
+    password: changeme
+    username: elastic
+
+---
+[default] FLEET_MONITORING:
+output:
+  elasticsearch:
+    hosts:
+    - 127.0.0.1:9200
+    password: changeme
+    type: elasticsearch
+    username: elastic
+programs:
+- filebeat
+
+---
+----