gRPC passes deadline information through the RPC boundary, but client and server have the same deadline. Ideally we'd like the server to have a slightly tighter deadline than the client, so if one of the server's onward RPCs or other network calls times out, the server can pass back more detailed information to the client, rather than the client timing out the server and losing the opportunity to log more detailed information about which component caused the timeout.
In this change, I subtract 100ms from the deadline on the server side of our interceptors, using our existing serverInterceptor. I also check that there is at least 100ms remaining in which to do useful work, so the server doesn't begin a potentially expensive task only to abort it.
Fixes#3608.