Add simple CLI to interact with Diun through gRPC
Create image and notif proto services
Compile and validate protos through a dedicated Dockerfile and bake target
Implement proto definitions
Move server as `serve` command
New commands `image` and `notif`
Refactor command line usage doc
Better CLI error handling
Tools build constraint to manage tools deps through go modules
Add upgrade notes
Co-authored-by: CrazyMax <crazy-max@users.noreply.github.com>
