Triage bulk import on EKS issues

We'd like to review the state of the following parent issue:
- https://github.com/gchq/sleeper/issues/7065

Bulk import on EKS is no longer documented as experimental, but there are still open issues on the parent issue.

We want to go over what's left, determine what needs to be done now, and move anything else to an appropriate place. Anything that needs doing now can be structured into workable issues, and left on the parent.

This issue needs attention to see what's changed since the original PR review, and writing up:
- https://github.com/gchq/sleeper/issues/7184

These issues need some manual testing to tell what's left to do:
- https://github.com/gchq/sleeper/issues/7068
- https://github.com/gchq/sleeper/issues/3451
- https://github.com/gchq/sleeper/issues/3480
- https://github.com/gchq/sleeper/issues/7540
- https://github.com/gchq/sleeper/issues/7642

Start by reviewing parent issue 7065 and the linked issue 7184 to understand the original PR review and current state. Manually test issues 7068, 3451, 3480, 7540, and 7642, then record what remains, move obsolete work appropriately, and leave any current work as actionable issues on the parent.

Written by the indexing model from the issue text.