Improve Documentation for connectors

[s0nicboOm]

Summary

Improve documentation for numalogic repository. Specifically, add a connectors tab in the User Guide to help them use the two fetcher classes we have namely Prometheus and Druid.

It could be something along this structure:

-> User Guide
----> Connectors
-------> Prometheus
-------> Druid

The docs directory is where most of the work needs to be done, and then the mkdocs.yml file needs to be updated to reflect any structure-level changes needed.

### Tasks
- [ ] Add Druid connector docs
- [ ] Add Prometheus Connector docs