PESDLC-1275 Use last modified date to clean bucket

[savex]

Improve bucket cleaning and use key object date instead of bucket one. Bucket date hold latest bucket modification that includes policy updates, uploads of new oblects, etc.

Backports Required

• [ ] none - not a bug fix
• [ ] none - this is a backport
• [x] none - issue does not exist in previous branches
• [ ] none - papercut/not impactful enough to backport
• [ ] v24.1.x
• [ ] v23.3.x
• [ ] v23.2.x

Release Notes

• none