[DocDB] Metrics for vector compaction and flush

[rthallamko3]

Jira Link: DB-18272

Description

Add metrics for vector compaction and flush related activities

Regular tables update the following compaction metrics:

• rocksdb_compact_read_bytes
• rocksdb_compact_write_bytes
• compaction_tasks
• rocksdb_compaction_times_micros_sum
• rocksdb_compaction_times_micros_count

Need to think through the below counts/ Introduce specific counters for vector chunks

• rocksdb_numfiles_in_singlecompaction_count
• rocksdb_numfiles_in_singlecompaction_sum

Some of them are relevant to vector indexes. It would be good to update them for vector compactions as well. At the same time, we should add new metrics that describe vector compactions better.

Issue Type

kind/enhancement

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[keisku]

@arybochkin 👋 Follow-up to #28842 which added vector_index_compact_write_bytes. Opened a #30360 to add the corresponding vector_index_compact_read_bytes for tracking input bytes read during vector index compaction.