Provide to a merge request CI pipeline a predefined variable reflecting a WIP status of the merge request

Problem to solve

At the moment there is no easy way to determine from merge request CI pipeline if the merge request is "Work-In-Progress". Yes, it can be done via API, but CI_JOB_TOKEN doesn't allow this access, so some other credentials have to be passed to the pipeline.

I guess it is pretty much understandable that there may be valid reasons to not execute (or executed only a subset of) pipeline on WIP MR-s.

Intended users

Each and every developer in projects with MR-based workflow.

Proposal

Provide a predefined variable, e.g. CI_MERGE_REQUEST_WIP set to one of true and false.

Permissions and Security

None.

Documentation

Add the variable description to Predefined environment variables reference/Variables

Availability & Testing

What does success look like, and how can we measure that?

What is the type of buyer?

Either Like to most of variables to the CE, or, like to CI_MERGE_REQUEST_TARGET_BRANCH_SHA to Premium/Silver.

Links / references