Add workflow to sync aws-vpc-cni helm chart to eks-charts

[fawadkhaliq]

What type of PR is this?

Enhancement

Which issue does this PR fix
#1319

What does this PR do / Why do we need it

Added a workflow to sync aws-vpc-cni Helm chart with eks-charts repo.

• Added a script to sync charts if there's a diff. This uses eks-bot to open a pull request on eks-charts repo that will need to be reviewed, approved and merged by the authors. In long term, we plan to deprecate the eks-charts repo and host the charts elsewhere (where? to be designed/decided)
• Added make target to sync on-demand and on release (includes release notes)
• Added GitHub Actions workflow to sync aws-vpc-cni Helm to eks-chart repo on VPC CNI release.

Same workflow as appmesh-controller. See ref: aws/eks-charts#444

Testing

• Test sync from fawadkhaliq/amazon-vpc-cni-k8s to fawadkhaliq/eks-charts repo:
  • https://github.com/fawadkhaliq/eks-charts/pull/4

Automation added to e2e
N/A

Will this break upgrades or downgrades. Has updating a running cluster been tested?:
N/A

Does this change require updates to the CNI daemonset config files to work?:
Nope

Does this PR introduce any user-facing change?
Nope

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[jayanthvn]

LGTM :)