[Bugfix] Fix 1-indexing for replica_id in MetricsStore

[sicario001]

Issue MetricsStore uses 1-indexing for replica_id at several places even though replica_ids are 0-indexed.

Fix Update 1-indexed usage of replica_id in _replica_memory_usage, _replica_busy_time and _replica_mfu inside MetricsStore to 0-indexed.

[AgrawalAmey]

@nitinkedia7 can you please take a look, thanks!

[nitinkedia7]

@sicario001 Please look at the comments I have left and also accept the Contributor License Agreement (without which the PR cannot be merged).

[sicario001]

@microsoft-github-policy-service agree

[AgrawalAmey]

@sicario001 @nitinkedia7 are we good to merge?