[EKS] [CoreDNS add-on]: Respect existing number of replicas during add-on update

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**Tell us about your request**
EKS add-on for CoreDNS to respect the current number of replicas of the deployment during updates.

**Which service(s) is this request for?**
EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
I would like the EKS add-on updates for CoreDNS to not revert to the default replica count of 2, but instead to respect the existing number of replicas, and complete a rolling update based off that value.

**Are you currently working around this issue?**
You can set the "replicaCount" add-on configuration to override the default value of 2.
For example, setting it to 5 would override the default value of 2. If "autoscaling.minReplicas" is set to 10 and "replicaCount" is set to 5, it will terminate 5 pods to meet replicaCount, then scale up to 10 to meet autoScaling minReplicas.

This would not be required if the deployment respected the existing number of replicas.

**Additional context**
To replicate the issue:
1. Update the EKS add on to use autoscaling with minReplicas 5
2. Observe it auto-scale to 5 replicas (from default 2)
3. Make an update to the EKS add-on configuration (can be whitespace change)
4. Observe that it drops the replica count down to 2 (default value), and then back up to 5 (minReplicas value) in < 1 min

**Attachments**
N/A

Start with the EKS CoreDNS add-on update behavior described in the issue, focusing on how the existing replica count, replicaCount, and autoscaling.minReplicas interact. Reproduce the listed update sequence and verify that an update preserves the current count and completes without the temporary drop to the default of two replicas.

Written by the indexing model from the issue text.