We offer 10GB of free cache storage per repository each week, similar to
GitHub's approach.
Any cache that hasn't been accessed in the past 7 days is removed.
Furthermore, when cache usage exceeds 10GB, we delete the oldest cache
until the usage falls below 10GB.
GithubRepositoryNexus already checks for jobs every 5 minutes. I think
it can check cache usage too. If we find that every 5 minutes is too
frequent, we can adjust this timing in the future.
0d61c8ec7d