Add loading row to pipelines table

What does this MR do and why?

Skeleton loader task for iteration 1 of async pipeline creation

Add loading row to pipelines table for async pipeline creation.

This is only for the merge request pipelines table.

Screenshots or screen recordings

full screen	mobile

How to set up and validate locally

1. Go to a merge request with pipelines
2. In the pipelines tab, click "Run pipeline"
3. The first row of the table should be skeleton loaders until the pipeline is created and appears.