[Feature Request] Set hard limits for CLIProxyAPI API Keys

[DevGuyRash]

I was planning to run a few n8n automations that use the proxy server as a backend. It got me thinking though about a nice feature to have for if people ever decide to use this across many services:

The ability to set a hard request limit or token limit for an individual api key. Maybe it could even set them per provider or even set allowed providers for that api key.

For me, this would make it so that if I have a chatbot then someone isn't just talking to it all day and using up all of the usage just for fun.

Appreciate the hard work your team does!