Rename ci/cd minutes to compute in purchase pages

What does this MR do and why?

This renames the purchasing-related pages from CI/CD minutes (and similar) to compute or units of compute, as needed.

• Related to https://gitlab.com/groups/gitlab-org/-/epics/9503+
• Related to [Docs] "CI minutes" > "compute minutes" (#407063 - closed)
• Related to "CI minutes" > "compute minutes" (gitlab-com&2150 - closed)

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