This commit adds domain-scope to the scope_types for limit policies,
allowing domain users to access those APIs when enforce_scope is
enabled. This commit also introduces some tests that explicitly show
how domain users are expected to behave with the limits API. A
subsequent patch will do the same for project users.
This commit also modifies the GET /v3/limit policy to allow project
users to filter responses by project_id, which isn't entirely useful
outside of just calling the API with a project-scoped token.
Change-Id: I9b38f3fd2f83efd508b2d9a6c323bbaa7169d4cd
Related-Bug: 1805880
Partial-Bug: 1818736