Add e2e test of storage size changes

The discussion in gitlab-org/gitlab#357680 (closed) highlights the importance of accurately reporting storage usage that users have control over.

There seems to be mostly-sufficient automated tests in place, but none that use real files as input. An end-to-end test would provide more confidence that we can catch regressions, particularly in the case of a mismatch between Gitaly and GitLab Rails versions.

The test should include changes to a repository that could affect the storage size reported in unexpected ways, like those discussed in gitlab-org/gitlab#357680 (closed) and https://gitlab.com/gitlab-org/gitlab/-/issues/351415

The test should use the default housekeeping options and should account for those settings when checking for changes to the reported storage size.