Resolve "Stork cannot connect large Kea installation"

Closes #398 (closed)

For now I just introduced gzipping a content that is transmitted over gRPC. Bigger contents get pretty well compressed e.g. from 4MB to 40kB. If this problem reappears then I would increase gRPC message size limits to 100MB. It shouldn't cause performance problems but for sure will be enough to transmit any Kea config.