Add support to configure branch ENI cooldown period via configmap

[sushrk]

Issue #, if available:
#306

Description of changes:
Adding support to configure the cool down period via amazon-vpc-cni configmap using flag branch-eni-cooldown, in seconds. The minimum value for the cool period is 30s, if user updates configmap to a lower value, this will be overridden and set to 30s.

Testing updated in comments.

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[haouc]

@sushrk made some changes in the new commit. please let me know if you have comments on them. I will ask for reviews from the team.

[haouc]

We allow the period configurable but force the lowest value as 30 seconds. Whenever the value is changed, the controller broadcast a node event to all nodes which ensure users the planned value being applied successfully.
Testing some behaviors
Setting cooldown period to 120 seconds

Events:
  Type    Reason                          Age   From                     Message
  ----    ------                          ----  ----                     -------
  Normal  ControllerVersionNotice         11m   vpc-resource-controller  The node is managed by VPC resource controller version v1.4.2-9-gf21a4f9
  Normal  NodeTrunkInitiated              11m   vpc-resource-controller  The node has trunk interface initialized successfully
  Normal  BranchENICoolDownPeriodUpdated  41s   vpc-resource-controller  Branch ENI cool down period has been updated to 2m0s

Then change the value to 29 seconds which should be forced to 30 seconds although CM still has 29 seconds

apiVersion: v1
data:
  branch-eni-cooldown: "29"
  enable-network-policy-controller: "false"
  enable-windows-ipam: "false"
kind: ConfigMap
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"v1","data":{"enable-network-policy-controller":"false","enable-windows-ipam":"false"},"kind":"ConfigMap","metadata":{"annotations":{},"labels":{"app.kubernetes.io/instance":"aws-vpc-cni","app.kubernetes.io/name":"aws-node","app.kubernetes.io/version":"v1.15.4","k8s-app":"aws-node"},"name":"amazon-vpc-cni","namespace":"kube-system"}}
  creationTimestamp: "2023-12-02T19:56:21Z"
  labels:
    app.kubernetes.io/instance: aws-vpc-cni
    app.kubernetes.io/name: aws-node
    app.kubernetes.io/version: v1.15.4
    k8s-app: aws-node
  name: amazon-vpc-cni
  namespace: kube-system
  resourceVersion: "989462"
  uid: 1c7920ed-5d6b-452d-8228-f8dee3c771c8

Events:
  Type    Reason                          Age    From                     Message
  ----    ------                          ----   ----                     -------
  Normal  ControllerVersionNotice         15m    vpc-resource-controller  The node is managed by VPC resource controller version v1.4.2-9-gf21a4f9
  Normal  NodeTrunkInitiated              15m    vpc-resource-controller  The node has trunk interface initialized successfully
  Normal  BranchENICoolDownPeriodUpdated  4m12s  vpc-resource-controller  Branch ENI cool down period has been updated to 2m0s
  Normal  BranchENICoolDownPeriodUpdated  37s    vpc-resource-controller  Branch ENI cool down period has been updated to 30s

[jayanthvn]

Is this defaulted to 30s since if first time get fails what will be the value?