[DOCS] Relocate discovery module content (#56611) (#57454)

* Moves `Discovery and cluster formation` content from `Modules` to
`Set up Elasticsearch`.

* Combines `Adding and removing nodes` with `Adding nodes to your
  cluster`. Adds related redirect.

* Removes and redirects the `Modules` page.

* Rewrites parts of `Discovery and cluster formation` to remove `module`
  references and meta references to the section.

docs/reference/index.asciidoc

@@ -32,8 +32,6 @@ include::mapping.asciidoc[]
 
 include::analysis.asciidoc[]
 
-include::modules.asciidoc[]
-
 include::index-modules.asciidoc[]
 
 include::ingest.asciidoc[]

docs/reference/modules/discovery.asciidoc

@@ -1,11 +1,13 @@
 [[modules-discovery]]
 == Discovery and cluster formation
 
-The discovery and cluster formation module is responsible for discovering
+The discovery and cluster formation processes are responsible for discovering
 nodes, electing a master, forming a cluster, and publishing the cluster state
-each time it changes. It is integrated with other modules. For example, all
-communication between nodes is done using the <<modules-transport,transport>>
-module. This module is divided into the following sections:
+each time it changes. All communication between nodes is done using the
+<<modules-transport,transport>> layer.
+
+The following processes and settings are part of discovery and cluster
+formation:
 
 <<modules-discovery-hosts-providers>>::
 
@@ -15,17 +17,17 @@ module. This module is divided into the following sections:
 
 <<modules-discovery-quorums>>::
 
-    This section describes how {es} uses a quorum-based voting mechanism to
+    How {es} uses a quorum-based voting mechanism to
     make decisions even if some nodes are unavailable.
 
 <<modules-discovery-voting>>::
 
-    This section describes the concept of voting configurations, which {es}
-    automatically updates as nodes leave and join the cluster.
+    How {es} automatically updates voting configurations as nodes leave and join
+    a cluster.
 
 <<modules-discovery-bootstrap-cluster>>::
 
-    Bootstrapping a cluster is required when an Elasticsearch cluster starts up
+    Bootstrapping a cluster is required when an {es} cluster starts up
     for the very first time. In <<dev-vs-prod-mode,development mode>>, with no
     discovery settings configured, this is automatically performed by the nodes
     themselves. As this auto-bootstrapping is
@@ -67,10 +69,6 @@ include::discovery/voting.asciidoc[]
 
 include::discovery/bootstrapping.asciidoc[]
 
-include::discovery/adding-removing-nodes.asciidoc[]
-
 include::discovery/publishing.asciidoc[]
 
 include::discovery/fault-detection.asciidoc[]
-
-include::discovery/discovery-settings.asciidoc[]

docs/reference/modules/discovery/discovery-settings.asciidoc

@@ -1,7 +1,8 @@
 [[modules-discovery-settings]]
 === Discovery and cluster formation settings
 
-Discovery and cluster formation are affected by the following settings:
+<<modules-discovery,Discovery and cluster formation>> are affected by the
+following settings:
 
 `discovery.seed_hosts`::
 +

docs/reference/redirects.asciidoc

@@ -753,6 +753,39 @@ See <<cluster-shard-allocation-filtering>>.
 
 See <<misc-cluster-settings>>.
 
+[role="exclude",id="modules"]
+=== Modules
+
+This page has been removed.
+
+See <<settings,Configuring Elasticsearch>> for settings information:
+
+* <<circuit-breaker>>
+* <<modules-cluster>>
+* <<modules-discovery-settings>>
+* <<modules-fielddata>>
+* <<modules-http>>
+* <<recovery>>
+* <<indexing-buffer>>
+* <<modules-gateway>>
+* <<modules-network>>
+* <<query-cache>>
+* <<search-settings>>
+* <<shard-request-cache>>
+
+For other information, see:
+
+* <<modules-transport>>
+* <<modules-threadpool>>
+* <<modules-node>>
+* <<modules-plugins>>
+* <<modules-remote-clusters>>
+
+[role="exclude",id="modules-discovery-adding-removing-nodes"]
+=== Adding and removing nodes
+
+See <<add-elasticsearch-nodes>>.
+
 [role="exclude",id="_timing"]
 === Timing
 

docs/reference/setup.asciidoc

@@ -53,6 +53,8 @@ include::modules/cluster.asciidoc[]
 
 include::settings/ccr-settings.asciidoc[]
 
+include::modules/discovery/discovery-settings.asciidoc[]
+
 include::modules/indices/fielddata.asciidoc[]
 
 include::modules/http.asciidoc[]
@@ -109,6 +111,8 @@ include::setup/starting.asciidoc[]
 
 include::setup/stopping.asciidoc[]
 
+include::modules/discovery.asciidoc[]
+
 include::setup/add-nodes.asciidoc[]
 
 include::setup/restart-cluster.asciidoc[]