Update info on python support (#38855)

* Update the documentation to list Python 3 as official
* Add some reference targets for inventory variables so we can link to docs
* Add a platform FAQ section
  Populate it with

  * virtualenv info (previously on the python3 support page)
  * BSD (Link to the working with BSD page)
  * Solaris (Document how to work around the non-POSIX shell on some
    Solaris hosts)

  Fixes #21594

* Fix some refs in the release_and_maintenance document

* Fix unindent error in module template

Fix for the module/plugin template unintentionally unindented inside of
a raw block, leading to errors like:

ERROR: docs/docsite/rst/modules/redshift_facts_module.rst:289:0: Explicit markup ends without a blank line; unexpected unindent.

* Make wording for Solaris troubleshooting better.

docs/templates/plugin.rst.j2

@@ -261,10 +261,12 @@ Facts returned by this module are added/updated in the ``hostvars`` host facts a
                 <td>
                     <div class="cell-border">
                         {% if value.description is string %}
-                            <div>@{ value.description | html_ify }@</div>
+                            <div>@{ value.description | html_ify }@
+                            </div>
                         {% else %}
                             {% for desc in value.description %}
-                                <div>@{ desc | html_ify }@</div>
+                                <div>@{ desc | html_ify }@
+                                </div>
                             {% endfor %}
                         {% endif %}
                         <br/>