Add a DB function to delete all selectors for a profile

[jhrozek]

Summary

We'll do a dumb but easy way of updating selectors - we'll drop all
current for the profile being updated and re-add them.

Relates: #3723

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

there is a test + I cherry-picked the patch out 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: 54.402% (-0.005%) from 54.407%
when pulling b0c0f21 on jhrozek:selectors_delete_by_profile
into dccc11a on stacklok:main.

[dmjb]

Assuming that the number of selectors is generally small, and that the selectors themselves are small - I think this is a reasonable approach to updates.