feat: Role connections & subscriptions

[conorwastakenwastaken]

Adds role connections to Eris.

• Docs reference
• document role connections discord/discord-api-docs#5668)

Hopefully I haven't missed anything. I've checked both the docs and the above PR in the API GH repo (that Bsian kindly linked for me) but honestly the pr diff was a mess and hard to read so I could've missed something.

Also adds role subscriptions to Eris.

• Docs reference
• API PRs:
  • Document role subscriptions discord/discord-api-docs#5724
  • Document role subscription system channel flags and message field discord/discord-api-docs#5828

I need to add the message content for the role subscription message that Discord sends, but I've no idea wtf the content is so any help would be appreciated!

Additions:

• editRoleConnectionMetadataRecords() func in Client
• getRoleConnectionMetadataRecords() func in Client
• Message#roleSubscriptionData property
• Documented role_connections_verification_url property under OAuthApplicationInfo
• Obviously also added the necessary constants types, as well as the endpoint that the aforementioned functions use

[bsian03]

This is everything related to role connections

[bsian03]

role subscriptions