Change the Provider's FetchProperty/FetchAllProperties interface methods to look up by Properties, not just a name

[jhrozek]

Summary

The initial implementation of the FetchProperty/FetchAllProperties
methods was very github specific in the sense that it only allowed
looking up the entity by name. Other providers might not have a name and
the provider is best equipped to know what to look by.

Let's send Properties instead and let the provider pick the right ones
or return an error.

Related: #4171

Change Type

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

repo register + unit tests

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 53.692% (-0.01%) from 53.703%
when pulling c3b6967 on jhrozek:property_fetch_change_signature
into 02ab8b0 on stacklok:main.