Add bungie/domain/roblox connection types and correct SkuFlags.available

[MCausc78]

Description

Connection types:

• Bungie.net: https://github.com/discord/discord-api-spec/commit/d1a462342b5b3b021f4962e264eefd82dace9238 and https://github.com/discord/discord-api-docs/pull/6716
• Domain: https://github.com/discord/discord-api-docs/pull/6395
• roblox: https://github.com/discord/discord-api-spec/commit/526e07828d4cdb8e7ce105f2e46b6d7b1916a0db Sku flags: https://canary.discord.com/developers/docs/monetization/skus#sku-object-sku-flags

Connected issues & other potential problems

none

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [x] Ran dart analyze or make analyze and fixed all issues
• [x] Ran dart format --set-exit-if-changed -l 160 ./lib or make format and fixed all issues
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works