If the shotgun tests are executed for MRs, compare it against the MR's
base rather than the previous release. Only fail the job in case the
performance drops (pass on performance improvements).
Note that start_in optimization was removed, since it isn't properly
supported with rules as of February 2025
(https://gitlab.com/gitlab-org/gitlab/-/issues/424203). Without this
optimization, container test images are likely to be re-built
unnecessarily when testing different protocols. A workaround for the
.gitlab-ci.yml exists, but the extra complexity doesn't seem justified.
The container image builds might change or be optimized in the future,
so let's just go with the build duplication for now.
The shotgun performance tests are executed in a different repository, in
a couple of different pipelines. To hide away the complexity, this
script takes the pipeline ID of the triggered pipeline and then takes
care of the rest - waits for the pipeline to finish, locates the child
pipeline and the relevant results. The output from this script is a
convenient link to the charts with the results once they're available.
GitLab also has a mechanism which can wait for another pipeline.
However, it can't be utilized here, since there are variables which
need to be passed in when the pipeline is triggered (like protocol to be
tested, load, runtime etc.). This isn't currently supported by the
GitLab feature.
