Expose stats as json via embedded http server

## Description
The internal status, currently printed on the console at regular interval every x seconds should be exposed as json on a local webserver bound to `127.0.0.1`. This will allow to monitor the tool status in a generic way:

Reference:
- https://github.com/projectdiscovery/nuclei/issues/2811
- https://github.com/projectdiscovery/nuclei/issues/2982