Deduplicate ManageViaMr specs [RUN AS-IF-FOSS]

What does this MR do?

The bulk of this deduplicates the ManageViaMr specs in order to make it easier to add tests for both FOSS and EE contexts.

This also introduces a small update to the ManageViaMr component: adding variant and category props to support #328385 (closed) (part of &5820 (closed)).

Finally, as a result of !58936 (merged) getting merged while this was first worked on, the last commit re-adds that work (but slightly tweaks it) that was lost as part of the rebase.

I recommend reviewing this MR on a commit-by-commit basis, and also by unchecking "Show whitespace changes" - though of course, feel free to review however you prefer 😄

Screenshots (strongly suggested)

n/a, no visual changes

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not 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.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• [-] I have tested this MR in all supported browsers, or it's not needed.
• [-] I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Related to #328385 (closed)