WIP 2.19 Porting Guide stub with data tagging

[nitzmahone]

We're linking to this PR as temporary documentation for the pending Data Tagging changes to core.

This PR won't include any other 2.19-specific Porting Guide entries. I assume once the feature has merged to devel, we'll merge this and create new PRs for other entries, or split an empty stub into a separate PR and merge it earlier if folks are champing at the bit to write non-DT Porting Guide entries.

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[ssbarnea]

@nitzmahone I managed to get very close with linter changes (only 10 test failures) but I spotted an unexpected exception when I call:

ModuleArgsParser(sanitized_task).parse( skip_action_validation=True) 

With 2.18 code, my call succeeds but with this PR it raises:

"Complex args containing variables cannot use bare variables (without Jinja2 delimiters), and must use the full variable style ('{{var_name}}')"

My task looks like:

{'name': 'Ansible-lint for args rule should succeed (Bug - 3199)', 'vars': {'copy_vars': {'src': 'args.json'}}, 'action': 'ansible.builtin.copy', 'args': '{{ copy_vars }}'}

I am not sure how to make it pass with 2.19.