Provide an endpoint to expose metrics to Prometheus #382
Description
Is your feature request related to a problem? Please describe.
To monitor the status of our AgentJ servers, we would like to extract some metrics.
Describe the solution you'd like
To avoid to create a dedicated page for metrics in the admin, we would like to create an endpoint that would expose metrics. This endpoint will be consumed by Prometheus (https://prometheus.io/) and charts created with Grafana.
We want to expose: number of incoming emails, number of spams and number of released emails.
The endpoint must be protected by HTTP authentication, with the credentials provided through the .env file.
Describe alternatives you've considered
N/A
Additional context
N/A