Language Worker Validation

There are validation steps that we should take to make sure that our language worker can actually run. For example, with Node, we need node path to be at a specific version of node.

**Solution proposal:**
We should add a path to a validation script in worker.config.json of each language worker.
The validation script should be a language-specific validation script and should `exit 0` on successful validation. On unsuccessful validation, the script should `exit 1` with appropriate error message
The functions host should find and run this validation script (async) and log the language-specific error message if validation is unsuccessful.

Likely, the validation will be run on worker startup failure for appropriate diagnostics.

cc: @pragnagopa