Review release pipelines of https://gitlab.com/tezos/tezos/-/blob/master/.gitlab-ci.yml

[tmcgilchrist]

Background

Octez tezos/tezos pipeline has a concept of a release pipeline, as a different type of pipeline to the regular builds for merge requests / branches. This task involves looking at the release pipelines and documenting the differences with a view to adding support for release pipelines into tezos-ci.