cloud storage/partition_recovery_manager: pass offset_map by value

[andijcr]

following https://github.com/redpanda-data/redpanda/pull/7157#discussion_r1022930410 modify how offset_map is passed to download_log_with_capped_size, to make the usage of iterator across suspension points more future proof

Backports Required

• [ ] none - not a bug fix
• [ ] none - issue does not exist in previous branches
• [x] none - papercut/not impactful enough to backport
• [ ] v22.3.x
• [ ] v22.2.x
• [ ] v22.1.x

Release Notes

• none