chore: gauge for flush compaction (#5156)

* add metrics

* chore/bench-metrics: Add INFLIGHT_FLUSH_COUNT Metric to Flush Process

 • Introduced INFLIGHT_FLUSH_COUNT metric to track the number of ongoing flush operations.
 • Incremented INFLIGHT_FLUSH_COUNT in FlushScheduler to monitor active flushes.
 • Removed redundant increment of INFLIGHT_FLUSH_COUNT in RegionWorkerLoop to prevent double counting.

* chore/bench-metrics: Add Metrics for Compaction and Flush Operations

 • Introduced INFLIGHT_COMPACTION_COUNT and INFLIGHT_FLUSH_COUNT metrics to track the number of ongoing compaction and flush operations.
 • Incremented INFLIGHT_COMPACTION_COUNT when scheduling remote and local compaction jobs, and decremented it upon completion.
 • Added INFLIGHT_FLUSH_COUNT increment and decrement logic around flush tasks to monitor active flush operations.
 • Removed redundant metric updates in worker.rs and handle_compaction.rs to streamline metric handling.

* chore: add metrics for remote compaction jobs

* chore: format

* chore: also add dashbaord