Description:

Currently an grpc access logger is instantiate using the creator' context. Usually the owner is an filter that can be destroyed.
The logger use the stats scope of the owner. It's fine if the logger is destroyed along with the owner.
However, the grpc access logger is expensive so that logger is cached. The logger can outlive its creator and the logger stats could refer a destroyed counter.

Since the grpc access loggers are shared for good, perhaps we should maintain an grpc access logger manager wide scope.
And generate server wide access_logs.grpc_access_log.logs_written.

Though we lost the detailed "<per_filter_prefix>.access_logs.grpc_access_log.logs_written" stats, but that counter is broken already when the cache is introduced.

cc @mattklein123 @ggreenway @jmarantz