Refactor MR page pipeline status check

What does this MR do?

Follow up from !65574 (comment 621991665).

I know we are having lots of transient bugs on the Merge Request page and we needed to be lenient with the pipeline status and others. I figured we could consolidate that to one place and have 1 wait logic as a baseline for the overall feature performance instead of having different wait logic in different places.

I also did some refactor around the related tests besides removing the wait logics to clean them up a bit.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Related to #335571 (closed)