all: trace streaming grpc calls

[crwilcox]

In order to quiet the logs as reported in #4133 we now only trace the time to first result for a streaming call. It may be interesting if we could trace/report on additional rpc calls.

This is a bit niche, and likely below in priority to finding a way to provide rpc traces for unary calls, but making a note here.

[codyoss]

Closing in favor of #4237