GetEntityByName must accept the type, too

[jhrozek]

Summary

Our database getter wouldn't handle the case where different entities
have the same name. Let's add the entity type as a parameter for the
getter.

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

make test + part of a larger branch

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: 53.715% (+0.01%) from 53.703%
when pulling 41d9e68 on jhrozek:prop_get_by_name_ent_type
into 2b9c305 on stacklok:main.