customizations

* Fix broken relative links for non-github pages like prometheus-operator.dev

* Update docs/customizations/developing-prometheus-rules-and-grafana-dashboards.md

Co-authored-by: Simon Pasquier <spasquie@redhat.com>

Co-authored-by: Zadjad Rezai <zadjad.rezai@kuehne-nagel.com>
Co-authored-by: Simon Pasquier <spasquie@redhat.com>