CodeQL integration (OSOE-734)

[BenedekFarkas]

See the official documentation.

It should be integrated into our workflows as a GitHub Action with reusable configuration for our typical usage scenarios.

As a built-in feature (repository setting), it's available for public repositories and can be enabled for all public repositories at once in the organization settings. It's only available for private repositories with Enterprise plan.

• Default setup
• Advanced setup (workflow)
• Doesn't check out submodules.
• Runs on a weekly schedule.
• None of the code in https://github.com/Lombiq/GitHub-Actions at the moment can be CodeQL-scanned.

Initial testing results with OSOCE:

• Superproject: JS/TS scanning came out green.
• Superproject: C# scanning failed, because the submodule projects are missing due to the submodules not being checked out + Could not auto-detect a suitable build method. See the logs for more details. (but this might be a results of the submodules missing).
• UITT: C# scanning failed, looks like it didn't restore NuGet packages.

Jira issue