Use native container healthcheck to determine gitlab readiness

What does this MR do and why?

Describe in detail what your merge request does and why.

docker context allows to run the whole docker workflow on an external machine that might not even be open to http traffic from outside. This scenario will be quite common for mac M1 users as currently we don't have arm omnibus image and the current one doesn't work natively on arm processors.

Current check for gitlab availability runs on host, thus it is not compatible with remote docker contexts.

This changes simply utilizes native omnibus image healthcheck to determine container readiness. It also means, if maintainers of omnibus image add additional checks, our tooling complies with that.

Also adds some rubocop todo fixes and improvements to output

MR acceptance checklist

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