Adopt ghi_clear variable name for clearsky GHI

[RDaxini]

• Relates to Standardise variable name for clearsky GHI and DNI, add to glossary #2272
• I am familiar with the contributing guidelines
• Tests added and modified
• Updates entries in docs/sphinx/source/reference for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

Also related: #1253, #2274

[RDaxini]

Change to haurwitz is non-user facing so the variable name is changed directly (non-breaking change)
Other changes are breaking changes. So far tried adding a test to test_irradiance.py (multiple attempts, here in this pr is the latest version...) but this fails (no warning emitted). Could I get some help with this, please? Not sure if the test is incorrect or the use of renamed_kwarg_warning is incorrect. I am pretty lost here:(

[echedey-ls]

I am pretty lost here:(

Kinda my fault for not documenting what I thought was obvious, sorry 😬
You have to rename the variables in the signature, see suggestions.

[AdamRJensen]

I recommend that you hold on working concurrently on this PR (#2306) and #2274 as they concern many of the same functions and will create a headache to merge.

[echedey-ls]

Ignore the comment below, PR nailed, @RDaxini ! Well done using that random, undocumented decorator.