This adds a Gateway Mesh section to the web-interface (+ API endpoints)
to see the status op each Relay Gateway within the Gateway Mesh.
The Gateway Mesh (https://github.com/chirpstack/chirpstack-gateway-mesh)
is an experimental feature to extend LoRaWAN coverage throug Relay
Gateways.
This needs to be tracked by git to make cargo publish work. If this
folder is in the .gitignore, then cargo publish will ignore this folder
as well and the publish command will fail because of missing .proto
files. If we would temporarily remove / rename the .gitignore file, then
cargo publish will error because the git state is dirty.
All these files can be generated using the `make api` command and there
is no real need to commit these into the repo. Only the api/go files
need to be comitted of how the Go import system works.
This also updates the Rust, Go, JS and gRPC-web (JS) code generation and
UI build to use the nix-shell environment instead of using Docker.
