Bump antsibull-docs version to 2.3.0 to support :ansplugin: and fix some aliases related bugs

[felixfontein]

See https://github.com/ansible-community/antsibull-docs/blob/main/CHANGELOG.rst#v2-3-0 for a detailled changelog.

The changes affecting the docs build are:

Features:

• Add a :ansplugin: role to the Sphinx extension. This allows to reference a module, plugin, or role with the fqcn#type syntax from semantic markup instead of having to manually compose a ansible_collections.{fqcn}_{type} label. An explicit reference title can also be provided with the title <fqcn#type> syntax similar to the :ref: role (Add plugin reference role to the Sphinx extension and use it ansible-community/antsibull-docs#180).
• When parsing errors happen in the Sphinx extension, the extension now emits error messages during the build process in addition to error markup (Sphinx extension: log build errors next to emitting error markup ansible-community/antsibull-docs#187).

Bugfixes:

• Make sure that all aliases are actually listed for plugins (Fix redirect finding and alias reporting ansible-community/antsibull-docs#183).
• When looking for redirects, the aliases field and filesystem redirects in ansible-core were not properly considered. This ensures that all redirect stubs are created, and that no duplicates show up, not depending on whether ansible-core is installed in editable mode or not (Fix redirect finding and alias reporting ansible-community/antsibull-docs#183).

[oraNod]

LGTM

[felixfontein]

@oraNod thanks for reviewing this!