k8s: Improve kubeReserved to handle Null max-pods

[gthao313]

Description of changes:
Improve kubeReserved to handle Null max-pods. When settings.kubernetes.max-pods returns Null, Bottlerocket should not reserve anything for kube-reserved.memory.

Testing done:
Since Those changes in different version kube-config are an identical change, and it works the same way in all versions, so we just need build aws-k8s-1.19-x86_64 and aws-k8s-1.19-aarch64 images to do test.

My repository does not have this change k8s: update eni-max-pods, so c6g.large is still qualified to be a test instance.

c6g.large
Userdata

[settings.kubernetes.kube-reserved]
memory = "100Mi"
cpu = "1"
ephemeral-storage = "2Gi"

bash-5.0# cat etc/kubernetes/kubelet/config
ca/etc/kubernetes
kubeReserved:
  cpu: "1"
  memory: "100Mi"
  ephemeral-storage: "1Gi"

Default

bash-5.0# cat etc/kubernetes/kubelet/config
ca/etc/kubernetes
kubeReserved:
  cpu: "70m"
  ephemeral-storage: "1Gi"

m5g.large ( we have this instance data)
default

kubeReserved:
  cpu: "70m"
  memory: "574Mi"
  ephemeral-storage: "1Gi"

Userdata

[settings.kubernetes.kube-reserved]
memory = "100Mi"
cpu = "1"
ephemeral-storage = "2Gi"

bash-5.0# cat etc/kubernetes/kubelet/config
ca/etc/kubernetes
kubeReserved:
  cpu: "1"
  memory: "100Mi"
  ephemeral-storage: "1Gi"

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.