In preparation for supporting the OpenTelemetry protocol for the proxy's traces, this vendors the relevant protobufs as well as some convenience helpers here.
This works around the fact that the existing `opentelemetry` crates do not support the version of tonic that we currently use (0.10), and this vendoring can be removed once we update.
[#10111](https://github.com/linkerd/linkerd2/issues/10111)
Signed-off-by: Scott Fleener <scott@buoyant.io>
Scott Fleener