Feature request: get ".proto" file from URI

[andresvia]

Often I find myself downloading a .proto file from the webz just to pass it to grpcurl, I know I can easily script it out but could probably be nice to have it as a grpcurl feature.

Example:

old workflow:

wget --continue https://raw.githubusercontent.com/grpc/grpc/master/src/proto/grpc/health/v1/health.proto 
grpcurl -proto health.proto -plaintext  127.0.0.1:8080 grpc.health.v1.Health/Watch  

new workflow

grpcurl -proto https://raw.githubusercontent.com/grpc/grpc/master/src/proto/grpc/health/v1/health.proto -plaintext  127.0.0.1:8080 grpc.health.v1.Health/Watch