Refactor per-PRC limiters to prepare for adaptiveness integration
A part of #5615 (closed)
This MR performs some refactorings before integrating the adaptive calculator into per-RPC limiting including:
- Implement a validation function for the
concurrency
setting. - Let
limithandler.WithConcurrencyLimiters
return created limits. Those limits will be integrated with the calculator in a later MR.
Those changes don't change the behavior of per-PRC limiter.
Edited by Quang-Minh Nguyen