Move to using k8s StatefulSets when deploying instances

We currently create a k8s Deployment when deploying a Node-RED instance in the platform.

As part of the roadmap to HA (see https://github.com/flowforge/flowforge/issues/1920) we need to migrate to using StatefulSets. This will allows us to run two copies of the instance in an active/stand-by configuration.

We only recently moved to using Deployments rather than bare pods, so already have some code in place to deal with migration as instances are suspended/resumed.

For this task the requirements are:

- [ ] Any new instance should be created as a StatefulSet
- [ ] Existing instances, whether still a bare pod or deployment, should get recreated as a StatefulSet when it is next suspended/resumed