Docs: correct search API (#7756)

This closes #7718. It corrects some inaccuracies and adds
an explanation of the truncations block.

website/pages/api-docs/search.mdx

@@ -8,9 +8,9 @@ description: The /search endpoint is used to search for Nomad objects
 # Search HTTP API
 
 The `/search` endpoint returns matches for a given prefix and context, where a
-context can be jobs, allocations, evaluations, nodes, or deployments. When using
-Nomad Enterprise, the allowed contexts include quotas and namespaces.
-Additionally, a prefix can be searched for within every context.
+context can be jobs, allocations, evaluations, nodes, deployments, plugins,
+or volumes. When using Nomad Enterprise, the allowed contexts include quotas
+and namespaces. Additionally, a prefix can be searched for within every context.
 
 | Method | Path         | Produces           |
 | ------ | ------------ | ------------------ |
@@ -36,14 +36,15 @@ job related results will not be returned. If the token is only valid for
   matches might be "abcd", or "aabb".
 - `Context` `(string: <required>)` - Defines the scope in which a search for a
   prefix operates. Contexts can be: "jobs", "evals", "allocs", "nodes",
-  "deployment" or "all", where "all" means every context will be searched.
+  "deployment", "plugins", "volumes" or "all", where "all" means every
+  context will be searched.
 
-### Sample Payload (for a specific context)
+### Sample Payload (for all contexts)
 
 ```javascript
 {
   "Prefix": "abc",
-  "Context": "evals"
+  "Context": "all"
 }
 ```
 
@@ -61,20 +62,38 @@ $ curl \
 ```json
 {
   "Matches": {
-    "evals": ["abc2fdc0-e1fd-2536-67d8-43af8ca798ac"]
+    "allocs": null,
+    "deployment": null,
+    "evals": ["abc2fdc0-e1fd-2536-67d8-43af8ca798ac"],
+    "jobs": ["abcde"],
+    "nodes": null,
+    "plugins": null,
+    "volumes": null
   },
   "Truncations": {
-    "evals": "false"
+    "allocs": "false",
+    "deployment": "false",
+    "evals": "false",
+    "jobs": "false",
+    "nodes": "false",
+    "plugins": "false",
+    "volumes": "false"
   }
 }
 ```
 
-### Sample Payload (for all contexts)
+#### Field Reference
+
+- `Matches` - A map of contexts to matching arrays of identifiers.
+
+- `Truncations` - Search results are capped at 20; if more matches were found for a particular context, it will be `true`.
+
+### Sample Payload (for a specific context)
 
 ```javascript
 {
   "Prefix": "abc",
-  "Context": ""
+  "Context": "evals"
 }
 ```
 
@@ -92,18 +111,10 @@ $ curl \
 ```json
 {
   "Matches": {
-    "allocs": [],
-    "deployment": [],
-    "evals": ["abc2fdc0-e1fd-2536-67d8-43af8ca798ac"],
-    "jobs": ["abcde"],
-    "nodes": []
+    "evals": ["abc2fdc0-e1fd-2536-67d8-43af8ca798ac"]
   },
   "Truncations": {
-    "allocs": "false",
-    "deployment": "false",
-    "evals": "false",
-    "jobs": "false",
-    "nodes": "false"
+    "evals": "false"
   }
 }
 ```