gRPC file upload service

To run the service

go run cmd/main.go

Clients can upload files by streaming FileChunks. Server accepts default size payloads (4MB). Uploaded file will be placed in a current working directory. Uploaded file will be named uploaded-file-<timestamp>. If uploaded contents contain a valid JSON structure, it will be mutated and written o a file named uploaded-file-mutated-<timestap> in cwd.