chore: add linter for graphql queries

What does this merge request do and why?

After I missed a bracket in graphql query that caused an error, there were a proposition to lint our graphql queries to avoid problems like this

#1653 (closed)

Important

This MR was build with Duo CLI.

How to set up and validate locally

• ask in agentic chat question like what is description of: http://gdk.test:3000/gitlab-duo/test/-/work_items/144
• observe answer - it should be without any errors
• in agentic chat, ask it to create or update work item

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.
• If this change requires executor implementation: verified that issues/MRs exist for both Go executor and Node executor or confirmed that changes are backward-compatible and don't break existing executor functionality.