To reduce CI times from ~10 mins to ~5:

This requires:

• Moving from docker compose v1 (docker-compose) to v2 (docker compose), which bring support for cache_to and cache_from settings.
• Using the non-default docker builder (`docker-container), which supports different caching methods, like the Github Actions cache.

Given the above involves a slightly more complicate CI, less backward-compatible, an alternative approach would be to move the build of the spdk and ceph images outside the nvmeof repo:

• Having the ceph vstart cluster built outside is not a wild idea: it barely changes, and it could be reused by other projects. Also that enforces the idea of single repo, single service (thus single container).
• Same for the spdk container, which is unfrequently changed.