High availability mode for Helm deployments

As part of getting started with Kubernetes monitoring, you might want to configure high availability. When you're finished, you can return to the installation instructions for your helm deployment.

As for now, this feature is limited to Helm deployments.

The high availability mode offers the following capabilities:

Increases replicas to two replicas for webhook deployment.
Adds pod topology spread constraints:
- Pods are spread across different nodes, with the nodes in different zones where possible.
- Multiple pods are allowed in the same zone.
Adds pod disruption budget:
- It restricts graceful shutdowns of the webhook pod if it's the last remaining pod.

To enable this, add the following to values.yaml:

webhook:
  highAvailability: true