Allow client to specify endpoint buffer size

## Feature Request

### Crates

Tonic

### Motivation

Some endpoints need to specify a specific buffer size for compatibility with 3rd party GRPC implementations.

### Proposal

Add a setter for the `buffer_size` field in the `Endpoint` struct, in the same fashion other fields can be setup.

### Alternatives

Fix other 3rd-party GRPC implementations that require a fixed / larger buffer size (incl. closed-source)