Support for pipelines for merge requests

[dersvenhesse]

Hi there,
we're using detached pipelines for merge requests in our projects.

The way I see it, these pipelines are not supported since the fetching happens via project branches. To list detached pipelines as well, the MRs and their pipelines need to be fetched: https://docs.gitlab.com/ee/api/merge_requests.html#list-mr-pipelines.

Do you think this would be useful feature?