Use protobuf plugin

[disc99]

Currently, it directly references the jar file.
Want to use this setting via plugin.

protobuf {
    protoc {
        artifact = "com.google.protobuf:protoc:${protobufVersion}"
    }
    plugins {
        grpc {
            // ...
        }
        webflux {
            artifact = "..."
        }
    }
    generateProtoTasks {
        all()*.plugins {
            grpc {}
            webflux {}
        }
    }
}