Fix Alloy pushing metrics to prometheus

Motivation

Currently, Alloy attempts to push metrics to prometheus but receives a 404 from Prometheus. It seems that Alloy isn't pushing on the correct path as other components push to prometheus with /api/v1/push and alloy is attempting to use /api/prom/push.

These errors are visible in the Alloy logs:

alloy ts=2024-09-11T19:35:53.705965331Z level=error msg="non-recoverable error" component_path=/ component_id=prometheus.remote_write.metrics_service subcomponent=rw remote_name=2cb11b url=http://monitoring-monitoring-kube-prometheus.monitoring.svc.cluster.local:9090/api/prom/push count=1380 exemplarCount=0 err="server returned HTTP status 404 Not Found: 404 page not found"

Acceptance Criteria

• Alloy's logs don't show any errors pushing metrics to Prometheus
• Metrics originating from Alloy show up in Prometheus