Add Metrics endpoint

[Jaydee94]

The Application should get a metrics endpoint with the following metrics:

• Number of sealing operations
• Flask metrics: https://pypi.org/project/prometheus-flask-exporter/

https://dev.to/camptocamp-ops/implement-prometheus-metrics-in-a-flask-application-p18

The Helm Chart should get a optional value for automatically generating a ServiceMonitor for collecting the metrics with a kubernetes internal prometheus.