Fix configureGamePass

[Regalijan]

• Use new endpoint
• Fix request dying because of non-string form values
• Don't tell Roblox it's a PNG when it isn't

Error handling could be a bit better but I'm saving that for #800

[Neztore]

I'm happy but won't merge since I see there's a pending review from Alan

[alanbixby]

This needs updated typings documented; the old response is a Promise<GamePassResponse>, but it appears the new endpoint would be a Promise<void>.

This should be documented in the local JSDocs comment, typings/jsDocs.ts, and typings/index.d.ts

[alanbixby]

Retracting comment about types - the response is manually returning data about the endpoint, so the return type is the same. No updates to types needed.