Add UET BuildConfig.json schema to catalog

[hach-que]

This adds a catalog entry for UET's BuildConfig.json format. UET is an unofficial tool for building Unreal Engine plugins, projects and the engine itself.

The referenced schemas are automatically generated from the C# types and committed to the UET schema repository, so they are always up-to-date and correct.

[madskristensen]

Thanks

[hach-que]

Do you know how long it takes for VS Code to pick up the new schemas from Schema Store? It doesn't appear to be immediate and it'd be good to know roughly when this will propagate.

[madskristensen]

I think it updates weekly, but there might be a way to force update it

[hach-que]

Thanks. I already gave the "Clear schema cache" command a shot but it didn't seem to work, so I'll wait out a week and see if it starts working.