gh-97517: Add documentation links to datetime strftime/strptime docstrings (#138559)

* Add documentation links to datetime strftime/strptime docstrings

- Add links to format codes documentation for all strftime methods
- Add links to format codes documentation for all strptime methods
- Addresses issue #97517

* Update C extension docstrings with format codes documentation

* Regenerate clinic code for updated docstrings

* Add clinic-generated header file for updated docstrings

* Fix docstring spacing consistency in both Python and C files

* Update Lib/_pydatetime.py

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>

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Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>