monitor docker hub official images for correct achitectures/images

MDEV-31529 highlighted that we can be without a sponsor's architecture a few months without noticing.

Docker hub has an API - docs.

Two useful urls are :

all tags, this is 520 items of released images. Little bit tricky to parse.

Single tag, like lts, latest. This seems quite simple to check there is 4 (different) architectures there (though 10.4 only has 3 - no s390x).

Note during release each architecture is pushed as its built so there's also a small window (of hours it seems - "last_pushed" in single tag api, where an incomplete set will be there.