Create standalone lint tool for rpc-config files

[ben-grande]

How to file a helpful issue

The problem you're addressing (if any)

The Qrexec Policy has a standalone lint tool, the rpc-config doesn't. It is very valuable to be able to lint a file at will instead of debugging, watching logs during runtime.

Initially discussed at #9176 (comment).

The solution you'd like

Create a rpc-config linter.

The value to a user, and who that user might be

• Developers that edits the rpc-config configuration will be benefit from this.
• Developers that modify the parser can verify more easily what the parser accepts.

Completion criteria checklist

(This section is for developer use only. Please do not modify it.)