Use k and cap_adjustment from Array.module_parameters in PVSystem.pvwatts_dc

[fuma900]

• Closes PVSystem.pvwatts_dc ignores k and cap_adjustment in module_parameters #2714
• I am familiar with the contributing guidelines
• I attest that all AI-generated material has been vetted for accuracy and is in compliance with the pvlib license
• Tests added
• 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.

[github-actions]

Hey @fuma900! 🎉

Thanks for opening your first pull request! We appreciate your
contribution. Please ensure you have reviewed and understood the
contributing guidelines.

If AI is used for any portion of this PR, you must vet the content
for technical accuracy.

[fuma900]

Since temp_ref wasn't documented and given the small footprint of the changes I haven't added any further documentation and/or updated the docstring. I think it might be useful to mention which keys of module_parameters are used though.

[RDaxini]

Thanks for your contribution @fuma900
I labeled the issue as a bug fix but now, thinking about it, was this ever working in a previous version?

[RDaxini]

Suggested change

	(:issue:`2714`, :pull:`2715`)
	(:issue:`2714`, :pull:`2715`)

You can add a line here to reduce the diff, which is what we would normally do. Not essential though

[cwhanse]

@RDaxini enhancement. This PR adds capability to the PVSystem method, which wasn't present before. It wasn't working but it wasn't claimed to be working, so not a bug in my mind.