Docs: Add a "seealso" section to the module docs (#45949)

* Docs: Add a separate  "seealso" section to the module docs
to list related modules and/or related references. This clears up the notes
section for things that are actual notes.

So you can add a section in your module documentation and four types of
references are possible.

    seealso:

    # Reference by module name
    - module: aci_tenant

    # Reference by module name, including description
    - module: aci_tenant
      description: ACI module to create tenants on a Cisco ACI fabric.

    # Reference by rST documentation anchor
    - ref: aci_guide
      description: Detailed information on how to manage your ACI infrastructure using Ansible.

    # Reference by Internet resource
    - name: APIC Management Information Model reference
      description: Complete reference of the APIC object model.
      link: https://developer.cisco.com/docs/apic-mim-ref/

This PR also includes:

- Implements ansible-doc support
- Implements schema support for the seealso options
- Updates to the development documentation
- Rename filter convert_symbols_to_format to rst_ify, cfr the existing html_ify and tty_ify filters
  - This makes the existing template a lot easier to read and fixes the confusion I had myself rereading the template (again).
- We fixed the possible suboption types (which was limited to 'bool' only)

* Use latest stable instead of devel docs

docs/bin/plugin_formatter.py

@@ -207,6 +207,7 @@ def get_plugin_info(module_dir, limit_to=None, verbose=False):
             :aliases: set of aliases to this module name
             :metadata: The modules metadata (as recorded in the module)
             :doc: The documentation structure for the module
+            :seealso: The list of dictionaries with references to related subjects
             :examples: The module's examples
             :returndocs: The module's returndocs
 
@@ -363,7 +364,7 @@ def jinja2_environment(template_dir, typ, plugin_type):
 
     templates = {}
     if typ == 'rst':
-        env.filters['convert_symbols_to_format'] = rst_ify
+        env.filters['rst_ify'] = rst_ify
         env.filters['html_ify'] = html_ify
         env.filters['fmt'] = rst_fmt
         env.filters['xline'] = rst_xline