Add CI job to build Rust files

[HCastano]

While updating the ink! tutorial I was manually building the code snippets and templates
to check that they still compiled.

However, this is not something that should be done manually since it is tedious and error
prone. Instead we should have a script which goes through everything and checks that it
build successfully. This script should be required to pass as part of the CI workflow.

Ensuring snippets compile might be a little tricky, but at the very least we should start
by checking that the x.x-finished-code.rs files compile correctly.

[nuke-web3]

This is part of a much larger goal: #478
I agree it would be a great thing for all of devhub, requires a refactor: the code snippets all live within the context of the latest version of the (various) node templates.