Use attributes to document module capabilities; warn about command module's check_mode support (#118)

* Improve formatting.

* Add 'api' action group attribute.

* Document attributes.

* Known issue: command module declares to support check mode.

* Compatibility with older ansible-core releases.

* Fix typo.

* Improve docs.

* Add shortcuts for common combinations.

* Update changelogs/fragments/command-check_mode.yml

Co-authored-by: Brian Scholer <1260690+briantist@users.noreply.github.com>

Co-authored-by: Brian Scholer <1260690+briantist@users.noreply.github.com>

plugins/modules/api_modify.py

@@ -24,12 +24,20 @@ description:
   - B(Note) that this module is still heavily in development, and only supports B(some) paths.
     If you want to support new paths, or think you found problems with existing paths, please first
     L(create an issue in the community.routeros Issue Tracker,https://github.com/ansible-collections/community.routeros/issues/).
-notes:
-  - Supports I(check_mode).
 requirements:
   - Needs L(ordereddict,https://pypi.org/project/ordereddict) for Python 2.6
 extends_documentation_fragment:
   - community.routeros.api
+  - community.routeros.attributes
+  - community.routeros.attributes.actiongroup_api
+attributes:
+  check_mode:
+    support: full
+  diff_mode:
+    support: full
+  platform:
+    support: full
+    platforms: RouterOS
 options:
   path:
     description: