Support for api/v9/guilds/<guildid>/members/supplemental

[hi117]

Discord added a new API to implement the members tab. It would be nice if bots could also consume this new API endpoint.

The requests look like this:
Path: api/v9/guilds//members/supplemental
Method: POST
Payload: {"user_ids":["id1", "id2", ...]}
Response: [{"user_id":"id1","source_invite_code":"code"},{"user_id":"id2","source_invite_code":"discovery_code"}, ...]

[ayn2op]

Reference: https://docs.discord.food/resources/guild#get-guild-members-supplemental