Migrate e2e tests to cover new stack with integrated auth

Now that we have landed integrated auth, we need to migrate our existing e2e test suite to cover the new auth flow and to make sure (at a minimum):

• New clusters are created as expected
• Namespaces are provisioned correctly/reliably with correct user permission model
• Namespace APIs have the correct authn/authz
• Namespace UI renders correctly for various authenticated users/tokens