Add helm values for Monitoring `ImagePullPolicy`

Currently imagePullPolicy is not set for most of, if not all of the monitoring CRs. We will need to evaluate each custom resource and add values where needed to override the pullpolicy. If values already are available, document them/add to here.

As an example:

• The prometheus CRD allows for setting imagePullPolicy under spec.containers.imagePullPolicy (see here - assuming I read correctly)
• We already provide a values passthrough in the prometheus template to allow values to be passed in for containers (see here)
• I would test that this override works by deploying monitoring with default values, checking the pull policy on prometheus pod(s), then deploying with a modified pull policy:

monitoring:
  values:
    prometheus:
      prometheusSpec:
        containers:
          imagePullPolicy: Always # Change to whatever is non-default

• Assuming this works, I would add this override to the table here.

I would repeat this process for every pod that is deployed as part of monitoring (looking into what deploys it - daemonset, deployment, CR, etc - and then whether we have a way to override the pull policy. If anything does not support it, we want to add that support.

AC:

• Monitoring pods (CRs/deployments) updated to allow for overriding the pull policy via helm values
• Ways to override the pull policies added/documented in the table here