Fix: show all DR tags in status when multiple DRs pull from the same …

[Adityakk9031]

FIX: #8316

Problem: When multiple DR tasks pull from the same primary, status details only shows 1 DR tag. All others are silently dropped.

Root Cause: Each fdbdr agent wrote all its tags under a single tags.$latest operator. When the cluster controller merged multiple agent status docs, $latest picked only the most recently updated agent's entire tags map, discarding the rest.

Fix: Move $latest from the tags-map level down to the individual tag level. Tags from different agents now merge as independent keys and no longer overwrite each other.

Files changed:

• fdbbackup/backup.cpp — getLayerStatus() for both AGENT and DR_AGENT branches.

[Adityakk9031]

@saintstack sir please have a look