Look into and/or implement OpenTelemetry context propagation

[hslatman]

What would you like to be added

After merging #391 we now include googleapis/google-api-go-client#2127. This allows OpenTelemetry context to be propagated through to GCP. crypto is probably not the right place for this issue, as it's not the "origin" for gRPC/HTTP clients/connections with options, but some operations pass through the package. It's more likely actual changes are to be made in https://github.com/smallstep/certificates/ and other users of this package.

Why this is needed

This will improve observability and help debugging things when using GCP infrastructure.

This is also related to things @azazeal has been working on, and might be working on in the (near) future.