Bug: Backend is restricting admins from creating File-backed HTTP Metadata Providers based on the admin group's regex

Steps to reproduce:

1. Login as admin
2. Set the admin group's regex to: /^foo.*$/
3. Create a provider
4. For entity id, enter anything not starting with "foo"
5. Attempt to save the provider

Expected result: The provider should save
Actual result: 400:

Also note that this provider type fails to persist (same error) whether the regex matches or not.