Rate Limit Error | Display rate limit text via dApps UI

[LlamaMB]

When we start dropping the limits, having a rate limit display message will be a good best practice. A lot of dApps show the said error message w/ text (attached).

Need: Add text for the rate limit Error 429 and outline how to get this text up on a dApp.

[BlinkyStitt]

I'm not sure what change the frontends need to make to do this. I think they need to add an error handler to the rpc queries they make that looks for error code 429.

We already give a message in our error response, but I could change it to be more specific to LlamaNodes:

https://github.com/llamanodes/web3-proxy/blob/main/web3_proxy/src/frontend/errors.rs#L165-L191