Fetch sources from parent project for MR pipelines and run on merge result
We should fetch sources from target project, instead of source project. We can still run on source project, but fetching on target with flexible ref specification allows us to seamlessly move to implementing test on merge result.
- We should pass to Runner
clone urlthat is of target project,
- We should pass as
/merge, the #47110 (closed)).
To make a runner to support flexible ref specifications we need to fix Runner: gitlab-runner!1092 (closed).
We also need to fix authentication scheme to allow use CI fork token to fetch sources from parent.
This allows us to seamlessly move to testing changes on merge results once the #47110 (closed) is implemented.
Note: This change is done in parallel with #23902 (closed)