[Feature] Add Support for Spacebar

[TheBrambleShark]

Description

This issue will act as a meta-issue for tracking progress for Spacebar support.

• Bring library support up to V10 - [Story] API v10 Feature Audit #362
• Allow consumers to specify endpoint addressses - [Spacebar] Allow client to accept alternative routes. #360
• Throw exception on startup if a user token is used for the official Discord API - [Spacebar] Add Discord Client Support #359
• Discuss how to handle missing routes in Spacebar
• Add additional package for handling restricted client routes - [Spacebar] Add Discord Client Support #359

Why This is Needed

Spacebar is a Discord-alternative service which is intended to be a FOSS, self-hosted, 1:1 reproduction of the Discord API. Because it is a 1:1 reproduction, this means that any applications using a Discord API library (Remora.Discord included), can connect to a Spacebar server instance and the bot will "just work."

This improvement will help account for users migrating to this alternative platform in light of the recent age verification changes.

Additionally, Spacebar supports custom client applications. Additional support is needed for Discord client endpoints, models, etc. Primarily, these changes should be implemented in a new Remora.Discord.Client library, which will handle a few restrictions.

Alternatives Considered

N/A

Additional Details

No response