remove cargo env var and improve code gen

[SuperFluffy]

It turns out that environment variables set inside .cargo/config are only seen by cargo if ran from the same workspace. The env vars are not seen if another 3rd crate imports this as a dependency, leading to compilation errors, leading to errors like:

error: environment variable `CARGO_WORKSPACE_DIR` not defined at compile time
 --> /home/runner/.cargo/git/checkouts/sequencer-relayer-8e1835a068793f96/a0172d3/sequencer-relayer/build.rs:3:38
  |
3 |     const PROTO_ROOT: &str = concat!(env!("CARGO_WORKSPACE_DIR"), "/proto/");
  |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: Cargo sets build script variables at run time. Use `std::env::var("CARGO_WORKSPACE_DIR")` instead
  = note: this error originates in the macro `env` (in Nightly builds, run with -Z macro-backtrace for more info)

Since there are other ways to solve this issue this config was removed in favor of:

1. creating a new crate sequencer-relayer-proto that owns the protobuf definitions and takes care of the rust codegen for protobuf;
2. moving the kubernetes yaml files into sequencer-relayer-test because that is were the files are used (nice extra: test-environment.yml is now generated from a test; as the main entry point for the integration tests it is now protected by CI).

[noot]

fixed my issue, thanks!!