Generate plugin rst (#28901)

Generate rst docs for plugins 

Based on rst generated for modules. But generated plugin
docs go into docs/docsite/rst/plugins/$PLUGIN_TYPE/plugin_name.rst
( docs/docsite/rst/plugins/connection/ssh.py for ex)

* move plugins docs to rst/*_plugins/ subdirs for namespace
* Only gen support pages for modules for now.
* Add generated plugin docs to gitignore* add list_*_plugins templates
* support MODULES/PLUGINS filters for make htmldocs

   Add a 'PLUGINS=ssh' filter env var like MODULES to filter plugins to build docs for.

* fixup 'historical' version_added, skip plugins/loader.py
* Fix plugins_by_support ref link to new plugins/*/ location
* use :ref: for common_return_values, allow empty version_added
* warnings on missing doc info
* add a prefix to _random_choice
  It was colliding with the target for random_choice plugin

docs/docsite/rst/index.rst

@@ -33,6 +33,7 @@ Ansible, Inc. releases a new major release of Ansible approximately every two mo
    modules_by_category
    vault
    command_line_tools
+   plugins_by_category
    guides
    dev_guide/index
    tower

docs/docsite/rst/intro_adhoc.rst

@@ -3,8 +3,6 @@ Introduction To Ad-Hoc Commands
 
 .. contents:: Topics
 
-.. highlight:: bash
-
 The following examples show how to use `/usr/bin/ansible` for running
 ad hoc tasks. 
 

docs/docsite/rst/intro_configuration.rst

@@ -3,7 +3,6 @@ Configuration file
 
 .. contents:: Topics
 
-.. highlight:: bash
 
 Certain settings in Ansible are adjustable via a configuration file.  The stock configuration should be sufficient
 for most users, but there may be reasons you would want to change them.

docs/docsite/rst/playbooks_loops.rst

@@ -408,7 +408,7 @@ Negative numbers are not supported.  This works as follows::
             state: present
           with_sequence: count=4
 
-.. _random_choice:
+.. _playbooks_loops_random_choice:
 
 Random Choices
 ``````````````