extproc: Implement client-side normal mode metrics (#9267)

This PR adds metrics for the normal mode implementation.

Also fixes:https://github.com/grpc/grpc-go/issues/9289 by adding
ResponseMode as Send so that we are able to catch the proc stream
failure because send can add all the messages to buffer and succeed
before the proc server can send End_Stream frame.
#ext-proc-a93

RELEASE NOTES: None