Add code owners for /shared/ and a catch-all

[owen-mc]

Currently no one is added as a reviewer, except in the /shared/quantum/ subfolder.

Talking points:

• Is it worth setting up some kind of team for this? I see that was done for ql-for-ql.
• Does anyone else want to be added? @MathiasVP maybe?

[Copilot]

Pull Request Overview

This PR adds code ownership for the /shared/ directory by assigning three specific reviewers as code owners. This addresses the current gap where no reviewers are automatically assigned for changes in the /shared/ directory (except for the /shared/quantum/ subfolder).

Key Changes

• Adds code ownership assignment for /shared/ directory to ensure automatic reviewer assignment

[nicolaswill]

The code in /shared/quantum/ is/should be owned by my team, @github/ps-codeql. I am the primary maintainer along with @bdrodes. It would be helpful for ongoing development to keep us as the code owner for that subdirectory. (edited for clarity)

[owen-mc]

@nicolaswill Yes, I have left the line related to that and my understanding is that because it is more specific lower down, it will override the rule I am adding for /shared/. (That's what copilot told me...)

[owen-mc]

I have created the team github/codeql-shared-libraries-reviewers.