Add pipeline in progress state MR widget pipeline

What does this MR do and why?

This MR adds an in-progress state to the MR pipeline widget. The goal is to have a UX state between when a user runs a pipeline on the MR and before the new MR widget pipeline subscription kicks in.

References

Screenshots or screen recordings

‼️ DEMO: https://www.youtube.com/watch?v=VPMpOTtcq-A ‼️

How to set up and validate locally

1. In rails console enable the feature flag

   Feature.enable(:mr_widget_pipeline_creation_state)

2. Visit a MR with CI pipelines
3. Run a MR pipeline and ensure in progress message shows
4. Ensure message disappears when new pipeline comes in
5. Test with commits etc as well.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #582554