UBI: move to ubi9, remove version from suffix

What does this MR do?

UBI: move to ubi9, remove version from suffix

Move to the use of UBI 9

Remove the numbered major version from the suffix of ubi. This changes
`ubi8` to `ubi` instead of `ubi9`.

Performed:
- for filenames: find | xargs git mv
- for contents: grep | xags sed

NOTE: This did not alter any packages installed / removed, or any syntax.
This change is relatively naive in that way.

Then, import learnings from previous checks:
https://gitlab.com/gitlab-org/build/CNG/-/merge_requests/1460

Related issues

Related to #2004 (closed)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated
• New dependencies are managed with dependencies.io