Enhancement: Create DiscordClientSandboxed for mods

[EliteMasterEric]

trafficstars

Issue Checklist

• [x] I have read the Contributing Guide
• [x] I have checked the Issues/Discussions pages to see if my enhancement has already been suggested
• [x] I have properly titled my enhancement

What is your suggestion, and why should it be implemented?

Implement a new DiscordClientSandboxed class, which grants access to a limited subset of the functions of funkin.api.discord.DiscordClient.

This would allow mods to alter the current state of the Discord RPC, while allowing API access to be removed or limited if any problems arise.