Add `Uri` to `tonic::Request`

## Feature Request

### Crates

`tonic`

### Motivation

A gRPC service may be accessible at multiple endpoints and knowing the hostname can be meaningful.

With HTTP1.1 this is usually available as the `Host` header and could have been accessed from the `MetadataMap`, but given the HTTP/2 context the right way to access this is the authority pseudoheader from the URI.

https://docs.rs/http/latest/http/request/struct.Request.html#method.uri
https://docs.rs/http/latest/http/uri/struct.Uri.html#method.authority

However, this is not currently available to tonic services.

### Proposal

Add a `uri: Uri` field to `tonic::Request` and a getter for it. This field should be copied over from the `http::Request`.

### Alternatives

A layer that adds the URI or required components (e.g. `request.uri().authority()`) as an extension.