Start renaming CI/CD minutes to compute credits

What does this MR do?

As per the related issues, the CI/CD minutes that you can purchase are renamed to compute credits, so we need to update the docs and UI to match.

This has already been changed in the user-facing marketing pages:

• https://about.gitlab.com/pricing/
• https://about.gitlab.com/pricing/faq-compute-credit/
• (etc)

So I think we really need to get this updated ASAP.

All instances of these terms need to be updated to compute credits:

• CI/CD minutes
• CI minutes
• pipeline minutes
• CI pipeline minutes
• minutes (when the context is about CI/CD minutes / compute credits)

This MR updates all UI text, docs, and specs to match the terminology we are now marketing to our users. It's a big one, but unfortunately I think it's the best solution to make sure nothing is missed and everything stays in sync. All the tests pass, and I verified as much as I could in the UI, you can see the before/after changes in the screenshots below.

Related issues

• Related to "CI minutes" > "compute minutes" (gitlab-com&2150 - closed)
• Resolves [Verify] Use "compute minutes" instead of "CI/C... (#342813 - closed)
• Resolves [Docs] "CI minutes" > "compute minutes" (#407063 - closed)

Screenshots

Instance settings:

• Before:
  
• After:
  

Admin settings for one group:

• Before:
  
• After:
  

Group usage page:

• Before:
  
• After:
  

Namespace usage page:

• Before:
  
• After:
  

** Buy Minutes page (/-/subscriptions/buy_minutes?selected_group=GROUP_ID) **

Before	After

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