Add in standard metrics for oracle

[kurt-google]

This adds in queries for some standard metrics in oracle to support basic alerting.

It also removes the busybox image from the monitoring container as it was only there for testing.

Users of Google Managed Prometheus with Managed Collection enabled on their GKE cluster (or who have manually configured a prometheus stack using the Prometheus Collector) can use this example PodMonitoring to ingest these metrics.

apiVersion: monitoring.googleapis.com/v1
kind: PodMonitoring
metadata:
  name: prom-elcarro
spec:
  selector:
    matchLabels:
      task-type: monitor
  targetLabels:
    fromPod:
      - from: instance
        to: db_instance
  endpoints:
  - port: 9187
    interval: 5m

Change-Id: I82560b65e7fa55bf3c67a3ab58d99180df6b1026

[akinfermo]

LGTM. Thanks!

[google-oss-prow]

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