Pipelines for new merge request

We added pipelines tab for merge requests in #18681 (closed), but whenever we're creating a new merge request, there's only builds tab but no pipeline tab.

Added frontend ~12980 labels

@godfat Good find, thanks! /cc @annabeldunstone

Reassigned to @annabeldunstone

mentioned in merge request !6238 (merged)

Mentioned in issue #22445 (closed)

Mentioned in merge request !6238 (merged)

Status changed to closed by merge request !6238 (merged)

Mentioned in commit d9273364

Mentioned in commit 9e2f3fd2