Set controller user-agent to vpc-resource-controller/git-version

[orsenthil]

Issue #, if available:

#442

The cloudwatch EKS cluster logs for vpc-resource-controller actions shows the userAgent field as:
"userAgent": "controller/v0.0.0 (linux/amd64) kubernetes/$Format",

Description of changes:

The controller user agent is set in the kubeConfig / client-go in this controller's case.

And it can be customized by updating .UserAgent of the kubeconfig used in making the call.

Testing.

1. Built the VPC RC Image with this change.
2. Deployed it to Beta Clusters
3. Verified it Audit Logs

fields @timestamp, @message, @logStream

| filter @logStream like /audit/

| filter requestURI like /cninodes/

After this change the userAgent will set to

        "@message": {
            "kind": "Event",
            "apiVersion": "audit.k8s.io/v1",
            "level": "Metadata",
            "auditID": "2e4b4b35-1aa0-4733-89c4-4xxx",
            "stage": "ResponseStarted",
            "requestURI": "/apis/vpcresources.k8s.aws/v1alpha1/cninodes?allowWatchBookmarks=true&resourceVersion=36132&timeoutSeconds=421&watch=true",
            "verb": "watch",
            "user": {
                "username": "eks:vpc-resource-controller",
                "groups": [
                    "system:authenticated"
                ]
            },
            "sourceIPs": [
                "10.0.97.217"
            ],
            "userAgent": "vpc-resource-controller/v1.5.0-11-gaabe5fd",

• there is no unit-test for the main module for this controller at the moment; this will require some refactor.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[haouc]

lgtm