This commit adds domain-scope to the scope_types for registered limit
policies, allowing domain users to access those API when enforce_scope
is enabled. This commit also introduces some tests that explicitly
show how domain users are expected to behave with the registered
limits API. A subsequent patch will do the same for project users.
Change-Id: I7a04e1e2fc585340c9e061c915461ab13b9abec2
Related-Bug: 1805880