Enable custom endpoints in Prometheus Service Monitor

**Image I'm using:** v1.4.0
**Issue or Feature Request:** Feature Request

Hey, guys! I would like to add as a suggestion for improvement in the Helm Chart, in the Service Monitor resource, the option to add custom `endpoints`, as it enables the configuration of some Grafana Cloud parameters.

https://github.com/prometheus-operator/prometheus-operator/blob/main/Documentation/api.md

Thanks!

Start with the Helm chart's ServiceMonitor resource and compare its supported fields with the Prometheus Operator API documentation linked in the issue. Done means the chart exposes configurable custom endpoints for the ServiceMonitor and supports the Grafana Cloud parameters described by the request.

Written by the indexing model from the issue text.