[DOCS] Relocate thread pools content (#55814)

Moves [thread pools content][0] from [Modules][1] to
[Configuring Elasticsearch][2].

Supporting changes:
* Changes page title to "Thread pools"
* Increments several headings
* Removes several unneeded `[float]` attributes
* Updates the anchors of several headings

Relates to #53307

[0]: https://www.elastic.co/guide/en/elasticsearch/reference/master/modules-threadpool.html
[1]: https://www.elastic.co/guide/en/elasticsearch/reference/master/modules.html
[2]: https://www.elastic.co/guide/en/elasticsearch/reference/master/settings.html

Co-authored-by: debadair <debadair@elastic.co>

Co-authored-by: debadair <debadair@elastic.co>

docs/reference/modules.asciidoc

@@ -41,15 +41,6 @@ The modules in this section are:
 <<modules-node,Node client>>::
 
     A Java node client joins the cluster, but doesn't hold data or act as a master node.
-
-<<modules-threadpool,Thread pools>>::
-
-    Information about the dedicated thread pools used in Elasticsearch.
-
-<<modules-cross-cluster-search, {ccs-cap}>>::
-
-    {ccs-cap} enables executing search requests across more than one cluster
-    without joining them and acts as a federated client across them.
 --
 
 
@@ -62,5 +53,3 @@ include::modules/gateway.asciidoc[]
 include::modules/http.asciidoc[]
 
 include::modules/node.asciidoc[]
-
-include::modules/threadpool.asciidoc[]

docs/reference/modules/threadpool.asciidoc

@@ -1,11 +1,9 @@
 [[modules-threadpool]]
-== Thread Pool
-
-A node holds several thread pools in order to improve how threads memory consumption
-are managed within a node. Many of these pools also have queues associated with them,
-which allow pending requests to be held instead
-of discarded.
+=== Thread pools
 
+A node uses several thread pools to manage memory consumption. 
+Queues associated with many of the thread pools enable pending requests 
+to be held instead of discarded. 
 
 There are several thread pools, but the important ones include:
 
@@ -35,7 +33,7 @@ There are several thread pools, but the important ones include:
 `write`::
     For single-document index/delete/update and bulk requests. Thread pool type
     is `fixed` with a size of <<node.processors, `# of allocated processors`>>,
-    queue_size of `200`. The maximum size for this pool is 
+    queue_size of `200`. The maximum size for this pool is
     `pass:[1 + ]`<<node.processors, `# of allocated processors`>>.
 
 `snapshot`::
@@ -94,15 +92,13 @@ thread_pool:
         size: 30
 --------------------------------------------------
 
-[float]
-[[types]]
-=== Thread pool types
+[[thread-pool-types]]
+==== Thread pool types
 
 The following are the types of thread pools and their respective parameters:
 
-[float]
-[[fixed]]
-==== `fixed`
+[[fixed-thread-pool]]
+===== `fixed`
 
 The `fixed` thread pool holds a fixed size of threads to handle the
 requests with a queue (optionally bounded) for pending requests that
@@ -123,9 +119,8 @@ thread_pool:
         queue_size: 1000
 --------------------------------------------------
 
-[float]
-[[scaling]]
-==== `scaling`
+[[scaling-thread-pool]]
+===== `scaling`
 
 The `scaling` thread pool holds a dynamic number of threads. This
 number is proportional to the workload and varies between the value of
@@ -143,9 +138,8 @@ thread_pool:
         keep_alive: 2m
 --------------------------------------------------
 
-[float]
 [[node.processors]]
-=== Allocated processors setting
+==== Allocated processors setting
 
 The number of processors is automatically detected, and the thread pool settings
 are automatically set based on it. In some cases it can be useful to override

docs/reference/setup.asciidoc

@@ -83,6 +83,8 @@ include::settings/transform-settings.asciidoc[]
 
 include::modules/transport.asciidoc[]
 
+include::modules/threadpool.asciidoc[]
+
 include::settings/notification-settings.asciidoc[]
 
 include::setup/important-settings.asciidoc[]