Frontend: Cannot provide manual variables to merge request pipeline

Summary

We recently added a Run Pipeline button to merge requests in order to allow you to start a merge request pipeline. This doesn't support, however, setting manual variables like you can through the Run Pipeline button under CI/CD->Pipelines.

Steps to reproduce

• Try to run a pipeline from the MR pipelines page and you are never presented with an opportunity to enter a manual variable
• Try to run a pipeline from the CI/CD->Pipelines page and you are presented with an opportunity to run a pipeline, but the pipeline does not run because it is an MR pipeline and the error you get is there are no jobs for the pipeline (and nothing runs.) This was the reason we created the other button.

Example Project

www-gitlab-com (though this would be the same on any.)

What is the current bug behavior?

You are not able to provide a manual variable.

What is the expected correct behavior?

You are able to.

Relevant logs and/or screenshots

N/A

Output of checks

This bug happens on GitLab.com

Possible fixes

Present the same dialog as when clicking on CI/CD->Pipelines->Run Pipeline as when you click on Run Pipeline from the MR.