Avoid code duplication in watch handlers on event

This commit makes the code of the on_event main function cleaner,
with no duplication and the same result.

Extend Prometheus metrics details

Fix on_event database update

This commit fixes the way database entries get updated after an
event. Since the resource "kind" is passed with capital initial
(i.e. "Deployment") we lowercase it so it can match the entries
(that are stored fully in lowercase).

Add support for insecure connections

This commit adds the INSECURE environment variable to make it
possible connecting Kubernetes instances without verifying
certificates.