[ENH] Alpha distribution

[SaiRevanth25]

What does this implement/fix? Explain your changes.

Implements Alpha Distribution. Towards https://github.com/sktime/skpro/issues/22 #### Does your contribution introduce a new dependency? If yes, which one? No #### Did you add any tests for the change? No #### PR checklist

For all contributions

• [ ] I've added myself to the list of contributors with any new badges I've earned :-) How to: add yourself to the all-contributors file in the skpro root directory (not the CONTRIBUTORS.md). Common badges: code - fixing a bug, or adding code logic. doc - writing or improving documentation or docstrings. bug - reporting or diagnosing a bug (get this plus code if you also fixed the bug in the PR).maintenance - CI, test framework, release. See here for full badge reference
• [x] The PR title starts with either [ENH], [MNT], [DOC], or [BUG]. [BUG] - bugfix, [MNT] - CI, test framework, [ENH] - adding or improving code, [DOC] - writing or improving documentation or docstrings.

For new estimators

• [x] I've added the estimator to the API reference - in docs/source/api_reference/taskname.rst, follow the pattern.
• [x] I've added one or more illustrative usage examples to the docstring, in a pydocstyle compliant Examples section.
• [ ] If the estimator relies on a soft dependency, I've set the python_dependencies tag and ensured dependency isolation, see the estimator dependencies guide.