Remove feature flag "command_stats_metrics", always enable feature
This MR removes the feature flag for command_stats_metrics which was introduced in !4464 (merged).
It's been rolled out to 100% of production traffic. The feature flag issue is #4175 (closed).
Please note that removing this feature flag will enable some new code paths. Since the flag is only checked in RPC context, commands that run outside of RPC context were previously not captured. Once this MR lands, they will be.
We have enough confidence from the RPC-level performance of the feature that we do not anticipate any issues with this rollout.
Edited by Igor