Notify about breaking changes in release notes

The problem was reported on the stork-users mailing list.

A user has updated the Stork server (1.12) but kept the previous version of the Stork agent (1.11). The Stork agent was not able to communicate with the server.

The problem was caused by changing the method of compressing the data exchanged between the agent and server.

We don't guarantee that the previous agent versions will work properly with the server's current version. However, we could warn users if any changes in the GRPC protocol are provided. It would make the update a bit smoother.