Make turning on zone redundancy an 'in place' change

**Is your feature request related to a problem? Please describe.**

Currently when you want to enable zone redundancy for an existing Spring Apps cluster, this can't be done 'in place', instead the full cluster needs to be recreated and all workloads need to be redeployed on the new cluster.

**Describe the solution you'd like**

It would be much more beneficial if the zone redundancy were a switch you can just enable on an existing cluster.

**Describe alternatives you've considered**

NA

**Describe the Customer Impact**

I see customers having issues with resilience and often it's because they did not use the zone redundancy feature during cluster creation. They are already far in using the cluster for multiple workloads. Turning on zone redundancy now is not possible on their existing cluster, which makes it a difficult process to increase their overall resilience, with potential downtime as a result.

**Additional context**

NA

**Can we contact you for additional details?** Y/N

Y

The issue mentions no files, tests, or entry points. Start by locating the existing Spring Apps cluster-creation and update paths, then determine how zone redundancy is represented and whether an in-place change is supported; done means enabling it without recreating the cluster or redeploying workloads.

Written by the indexing model from the issue text.