Verify runtime directory hash as part of CI

[CodeSandwich]

There's no mechanism preventing us from modifying the runtime without bumping its version.

In the GCS along the runtime file there should be a file following the same naming convention, but with a hash of the runtime and core directories. The CI should check if the current runtime version has its hash file in the GCS and if yes, it should assure that it matches the state of the code base. The CI should generate and upload the hash file when it uploads the corresponding runtime WASM file.

Open questions:

• How to hash 2 directories in a reproducible and portable way? Maybe git provides tooling fitting these criteria as a part of its plumbing.