Add support for service weighted target groups

[kellyyan]

Description

Amazon Web Services (AWS) is launching weighted target groups for Network Load Balancers (NLB). This feature allows users to configure static weights among multiple NLB target groups. Weighted target groups enable you to easily perform blue/green or canary deployment strategies with zero downtime and without the need of multiple load balancers.

Users can assign numeric weights between 0 and 999 to each NLB target group.

Use the following annotation to configure weighted target groups with your service:

    service.beta.kubernetes.io/actions.TLS-80: > 
    {
        "type": "forward",
        "forwardConfig": {
            "baseServiceWeight" : 20,
            # Forward to a service or existing target group
            "targetGroups": [
                {   
                    "serviceName": "service-1",
                    "servicePort": ,
                    "weight": 20,
                },
                {
                    "targetGroupARN": "arn:aws:elasticloadbalancing:us-east-1:xxxx",
                    "weight": 50
                }
            ],
            "targetGroupStickinessConfig": {
                "enabled": true
            }
        }
    }

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[k8s-ci-robot]

Hi @kellyyan. Thanks for your PR.

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[wweiwei-li]

/ok-to-test

[wweiwei-li]

/ok-to-test

[wweiwei-li]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kellyyan, wweiwei-li

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