Check periodically if remote backend file still exists

[BabyDino]

Is your feature request related to a problem? Please describe.
No.

Describe the solution you'd like
MAX_CACHE_SIZE works great keeping the cache small. However, when we are deleting a file from the remote backend, the cache is not informed and the file is still cached. It would be nice to check if the file still exists in the remote backend periodically ever x minutes/hours/days/weeks.

Describe alternatives you've considered
Removing files from the cache with cron, this is however not ideal.

Additional context
None.

[tharunn0]

Can i try to fix it and create a PR ? @BennyThink

[mathieu-aubin]

inotify or fswatch could also be an alternative i believe

also, maybe you could have an option to check for existing original file BEFORE doing the cache or convert for requests