Add support for iam.schlick to ModelChain

[cbcrespo]

• Closes Add support for iam.schlick to ModelChain #2828
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Currently, all direct IAM models available in pvlib.iam are supported by ModelChain except for schlick. This PR adds support for schlick.

[AdamRJensen]

@cbcrespo Given Anton's comment here I think we should also add a warning to the function itself (an admonition) stating something along the lines of:

The Schlick IAM model has not been validated for PV performance modeling and is not commonly used in PV applications. Users should consider these limitations when selecting models.

[RDaxini]

LGTM, just a note on pvsystem.py and the whatnsew. #2832 (comment) should also be addressed and then I think this PR is ready to go.

[kandersolar]

I think some tests for the PVSystem and Array methods would be good too. There should be existing tests that you can easily hook into like you did with the ModelChain tests.

One other thing: of course we can't infer schlick from the parameters (since it takes no parameters), but I suppose a comment in the inference function along those lines would be nice. Something here indicating that schlick is omitted on purpose:

https://github.com/cbcrespo/pvlib-python/blob/4ea1a645a46f6c373897a1d0436f9e21aa517b10/pvlib/modelchain.py#L801

[kandersolar]

Linter failure is on lines not touched by this PR