Report Tezos Octez build status into GitLab MR/commit

[tmcgilchrist]

Background

Currently the Octez pipeline is running on https://tezos.ci.dev but is not posting the build summary back to the MR/commit on https://gitlab.com/tezos/tezos.

Summary

We want to add a build summary and reporting stage to the pipeline to summarise the build result and post that plus a build status back to the merge request or commit.

eg When CI built merge request #5170 on tezos.ci.dev we want to post that build result back to the GitLab MR.

Outcome

Developers working on Tezos Octez implementation should see when their changes pass / fail the tezos-ci pipeline from the GitLab project.