docs: update autoscaling docs for the new query interface (#8917)

* update autoscaling docs for the new query interface
* update default value for query_window in scaling policy

website/pages/docs/autoscaling/plugins/apm.mdx

@@ -15,9 +15,7 @@ scaling should occur.
 ## Prometheus APM Plugin
 
 Use [Prometheus][prometheus_io] metrics to scale your Nomad job task groups or
-cluster. The query performed on Prometheus should return a single value. You can
-use the [scalar][prometheus_scaler_function] function in your query to achieve
-this.
+cluster.
 
 ### Agent Configuration Options
 
@@ -39,7 +37,7 @@ apm "prometheus" {
 ```hcl
 check {
   source = "prometheus"
-  query  = "scalar(avg((haproxy_server_current_sessions{backend=\"http_back\"}) and (haproxy_server_up{backend=\"http_back\"} == 1)))"
+  query  = "avg((haproxy_server_current_sessions{backend=\"http_back\"}) and (haproxy_server_up{backend=\"http_back\"} == 1))"
   ...
 }
 ```
@@ -74,20 +72,11 @@ configuration parameters take precedence over the environment variables.
 ```hcl
 check {
   source = "datadog"
-  query  = "FROM=2m;TO=0m;QUERY=avg:proxy.backend.response.time{proxy-service:web-app}"
+  query  = "avg:proxy.backend.response.time{proxy-service:web-app}"
   ...
 }
 ```
 
-The query consists of three sections, each separated using a `;` delimiter. More
-information on the arguments can be found on the [Datadog site][datadog_timeseries].
-
-- `FROM` - A time offset which indicates the start of the queried time period.
-
-- `TO` - A time offset which indicates the end of the queried time period.
-
-- `QUERY` - The query string to execute.
-
 ## Nomad APM Plugin
 
 The Nomad APM plugin allows querying the Nomad API for metric data. This provides

website/pages/docs/autoscaling/policy.mdx

@@ -57,6 +57,9 @@ horizontal application scaling or horizontal cluster scaling.
   should return a single value. Detailed information on the configuration options
   can be found on the [APM Plugins][apm_plugin_docs] page.
 
+- `query_window` - Defines how far back to query the APM for metrics. It should
+  be provided as a duration (e.g.: `"5s"`, `"1m"`). Defaults to `1m`.
+
 - `strategy` - The strategy to use, and it's configuration when calculating the
   desired state based on the current count and the metric returned by the APM.
   Detailed information on the configuration options can be found on the
@@ -84,6 +87,7 @@ policy {
   check "active_connections" {
     source = "prometheus"
     query  = "scalar(open_connections_example_cache)"
+    query_window = "5m"
 
     strategy "target_value" {
       target = 10