Delay/Schedule automated AMI updates

[preflightsiren]

Is this a BUG REPORT or FEATURE REQUEST?: Feature Request

Problem: When utilising #320 companies often have different tiers/channels of stability. Often they will want to have an AMI applied to development clusters, before being applied to production clusters.

Solution: Specify in configuration the amount of delay a cluster would like to add before updating the ASG configuration.

eg.

apiVersion: instancemgr.keikoproj.io/v1alpha1
kind: InstanceGroup
metadata:
  annotations:
    instancemgr.keikoproj.io/os-family: "amazonlinux2"
    instancemgr.keikoproj.io/lock-upgrades: "true"
    instancemgr.keikoproj.io/upgrade-delay: "7d"
  name: amazonlinux2-us-west-2b
  namespace: instance-manager
spec:
  eks:
    configuration:
      image: latest

Would update the image ID 7 days after the SSM parameter is changed.

[preflightsiren]

I've been thinking about this change over the last couple of days, and I think the best/most natural way to implement would be with: #320 + #321 , and an approver workflow or controller that approves after a period of time.