RPC server: do we need both `client.*` and `network.*` attributes on server spans

[lmolkova]

We have them on HTTP because peer can be a proxy and client represents client behind proxy.

For HTTP we have means (x-forwarded-for and such) to distinguish them and some RPC servers may find both useful (Dubbo, ConnectRPC that support pure HTTP clients).

For general RPC cases and gRPC it's probably less common to keep clients behind the proxy and also no standard mechanism to know original client IP, so the proposal is to remove client.* from common and gRPC attributes and add them later if there is a need.