[WIP] Enable Spacebar Support

[TheBrambleShark]

This PR will contain fixes to Remora.Discord to enable the following:

• Connect to a different server instance ([Spacebar] Allow client to accept alternative routes. #360)
• Expand the API surface for user endpoints restricted for use with user tokens. ([Spacebar] Add Discord Client Support #359)
• Ensure the library is brought up to compatibility with v9 of the API.
  • V10 support will come in a separate PR.

Fixes: #357
Fixes: #359
Fixes: #360