Fixes #5230: Adds CRUD permissions for GPG Keys.

Tested locally by the following:

1. Logging in as admin
2. creating a user with no permissions
3. logging into a different or incognito browser as that user
4. Adding one permission at a time to the user, and for each permission attempting to access GPG Keys and perform various operations
5. Navigating to Products and Repository pages as admin to ensure a list of GPG keys appears