In googleapis/java-spanner, we want to allow users set per-request timeout and retry settings.

Currently, the timeouts and retry settings are set at the time of client creation when the UnaryCallable is created (example). This means the retry settings are fixed per client instance. Our customers have requested for the ability to set RetrySettings per request, so that they may even be able to set them programmatically depending on the type of query that is being executed.

There is a discussion on this in #561 but I would like to create an explicit feature request for this.

Note that we have already brought this up with grpc-java and they asked us to follow-up here.

CC @ramiyer