Cleanup zimcheck S3 bucket

[benoit74]

This is a followup to openzim/zimfarm#1456

We need a background job to delete zimcheck files from S3 bucket when they are not needed anymore.

Since CMS is primary "user" of zimcheck data, it seems to make more sense the CMS is responsible to delete useless zimcheck files.

Once CMS has decided that zimcheck data is not needed anymore, probably the Zimfarm does not need it anymore either.

Zimfarm probably doesn't need to have read access to this data (it is only computing and writing this data, accessing it is more a convenience).