[catpkg] repository(Source)GzipUrl field in catpkg - link to gzipped catpkg.json

[amis92]

In the BSData/schemas#3 I've added a repositorySourceGzipUrl and repositoryGzipUrl which point to a pre-compressed (via gzip) catpkg.json asset.

This is the same file as repositoryUrl points to, except compressed. It might be good to use that endpoint to save bandwidth, especially for update checks.

Implemented in the BSData/publish-catpkg#8 (this is the GitHub Action that adds all needed assets to a release).

Implementation of repositorySourceUrl gzip alternative is tracked in BSData/gallery#5

This is an optional field. If not provided, app should fallback to the non-compressed URL as is used currently.