Add E2E test to verify the storage limits

For this test, we want to verify that the namespace goes into read-only when the storage limit is exceeded along with verifying that an in-app warning message is displayed. We want to modify the limit so that it is easier to hit the limit without having to create large files. As noted in customers-gitlab-com#6411 (comment 1440225302), we may want to run this in orchestrated since modifying a plan limit on staging has extra implications.