feat: make scope optional for user action validation

[dcoa]

The current PR enables the validation of user permissions without specifying a scope.

Context

openedx/wg-build-test-release#603

Merge checklist:
Check off if complete or not applicable:

• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Fixup commits are squashed away
• Unit tests added/updated
• Manual testing instructions provided
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

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