ci: Expose the coverage report and docs as links in the MR's

It's making handier to check how changes are tested and how docs are generated.

Sadly we can't expose more than one artifact yet so, we don't have much control on how and what we expose, but it's still more convenient than going through build jobs.

They should appear here once the pipelines are done.

Also adding support for native gitlab coverage analysis in MR's.