Clarify OTLP/gRPC endpoint configuration option handling

[pellared]

I've had users ask why the path is ignored for gRPC. Its not clear to new gRPC users that the path is derived from the proto spec for the service. Do you think its worth elaborating on that here and indicating which parts of the URL are honored for gRPC? Or maybe alternatively there's some gRPC doc we can point to?

Originally posted by @jack-berg in open-telemetry/opentelemetry-specification#3739 (comment)

I think that we can add a reference to https://github.com/grpc/grpc/blob/master/doc/naming.md. We can also add a notice that gRPC endpoint is NOT an URL therefore it does not understand e.g. the "path" URL component.

[pellared]

You can assign me to this issue and set appropriate labels.

[tigrannajaryan]

I am not sure this explanation belongs to spec. May be can be useful in https://github.com/open-telemetry/opentelemetry-proto/blob/main/docs/specification.md

[tigrannajaryan]

I guess it would be useful to have that sort of info on this page: https://opentelemetry.io/docs/concepts/sdk-configuration/otlp-exporter-configuration/

[austinlparker]

This is a documentation issue @svrnm @cartermp please assign appropriately

[svrnm]

Yeah, +1 what @tigrannajaryan suggested to have that mentioned in the SDK Configuration page, we might spread it from there to other pages

[pellared]

Unassigning myself as I continuously have other stuff which IMO has bigger priority.