support generate method invoke template

Although we can compse request param step by step，it would be more convenient if grpcurl can generate it automately.

### traditionally

step 1

```bash
➜ ~ grpcurl localhost:20789 describe grpc.health.v1.Health.Check
grpc.health.v1.Health.Check is a method:
rpc Check ( .grpc.health.v1.HealthCheckRequest ) returns ( .grpc.health.v1.HealthCheckResponse );

➜ ~ grpcurl localhost:20789 describe .grpc.health.v1.HealthCheckRequest
grpc.health.v1.HealthCheckRequest is a message:
message HealthCheckRequest {
string service = 1;
}
```

then make the request json, and invoke :

```bash
➜ ~ grpcurl -d '{"service": "test"}' localhost:20789 grpc.health.v1.Health/Check
{
"status": "SERVING",
"idle": 0.5,
"max_thread_count": 24
}
```

### newly

Suppose we support template command, and template will generate a invoke template

```bash
➜ ~ grpcurl localhost:20789 template grpc.health.v1.Health.Check
grpcurl -d '{"service": "test"}' localhost:20789 grpc.health.v1.Health/Check
```