Request caching + add ratelimit-over-408 + endpoint rewrite support

[cheesycod]

This PR adds support for (primitive) request caching for certain routes as well as the ability to 429 instead of 408 on a context deadline exceeded error. It also adds endpoint rewrite support which is useful in the instance where you may want to rewrite discord requests to other paths (for example, where the simple wsProxy string is not enough or if you have a seperate service for capturing state, an endpoint rewrite can be used to ensure all bots use it)

[cheesycod]

@germanoeich Tried resolving the changes