Add catpkg.json.gz asset file to uploads, link in catpkg.json as 'repositoryGzipUrl'

[amis92]

Schema: BSData/schemas#3

The catpkg.json should include links to both original and gzipped file (it's a lot of saved bandwidth, especially for a commonly pinged endpoint these files will become).

The .gz file should be an "optional" file, with the client app (BattleScribe) falling back to non-compressed json when gz is not available.

[amis92]

Gzip provides savings of about 85% (see BSData/gallery#5)

[amis92]

Example:

{
    "$schema": "https://raw.githubusercontent.com/BSData/schemas/master/src/catpkg.schema.json",
    "name": "wh40k",
    "description": "Warhammer 40,000",
    "battleScribeVersion": "2.03",
    "version": "v1.4.21",
    "lastUpdated": "2020-05-30T13:27:29Z",
    "lastUpdateDescription": "It was as if millions of SM voices all cried out in terror...",
    "indexUrl": "https://github.com/BSData/wh40k/releases/latest/download/wh40k.latest.bsi",
    "repositoryUrl": "https://github.com/BSData/wh40k/releases/latest/download/wh40k.catpkg.json",
    "repositoryGzipUrl": "https://github.com/BSData/wh40k/releases/latest/download/wh40k.catpkg.json.gz",
}

[amis92]

Schema: BSData/schemas#3