Add feature to implement tonic::transport::NamedService for middlewares

[davidpdrsn]

Tonic requires that services implement NamedService to be used with its router. I'm thinking it might be useful to have an optional feature called tonic that when enabled will add NamedService impls for all middleware as done here. Though it might require adding it to tower as well for it to actually be useful 🤔

[davidpdrsn]

I was able to find a solution in tonic that makes it easier to directly use any tower middleware without having to worry about NamedService hyperium/tonic#651