Rename indexes on GitLab.com

What does this MR do?

This fixes a bunch of naming inconsistencies with indexes on GitLab.com (production). We rename indexes here to align names with what we have in the codebase. See #296760 (closed) for details.

For regular installations that don't have these indexes, this is a no-op.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content