Support for custom podAnnotations, no hardcoded defaults

[fuine6]

Sorry, my english is poor.

Current hardcoded Annotations

prometheus.io/scrape: "true"
prometheus.io/port: {{ .Values.service.port | quote }}
prometheus.io/path: "/metrics"

Annotations I need

prometheus.io/scrape: "false"
prometheus.io/scrape_every_5s: "true"
prometheus.io/port: {{ .Values.service.port | quote }}
prometheus.io/path: "/metrics"

I need a way to override the default like this.