[Feature] Stats exporter for Prometheus

[d3vyce]

Hi 👋

My project is to integrate an stats exporter for prometheus. In short, a few features:

• on/off via admin
• endpoint protection for admins only
• export of challenges stats, scorebord, admin metrics, ...
• ability to add custom metrics for plugins

Basically, I was thinking of making a plug-in, but I think it would be a good addition to the project directly. So before starting development, I wanted to have a first feadback :)

[ColdHeat]

I think this is better started off as a plugin. One day it could be integrated into CTFd but it would be faster for your iteration for it to start off as a plugin.

[d3vyce]

Okay, I'll do that. As soon as the plugins are ready, I'll update this issue. If you like the feature, I can then integrate it into the project.