Golang image path customization in dockerfile to use Docker Proxy

[ridaz-zz]

What type of PR is this?
/kind enhancement

What this PR does / why we need it:
Due to dockerhub pull limit, internal registry can be used to fetch the golang image and deploy VDO.
This PR will bring in support to use docker proxy.

Which issue(s) this PR fixes:

Fixes #98

Test Report Added?:
/kind TESTED

Test Report:
Able to deploy VDO using docker proxy.

make deploy DOCKER_PROXY=harbor-repo.vmware.com/dockerhub-proxy-cache/library/

[builder 1/7] FROM harbor-repo.vmware.com/dockerhub-proxy-cache/library/golang:1.16@sha256:1e5f22f0c2efda5354823d26a9dde6802b753ec97156ee894d626721d33da3b8  

kubectl get pods -A

NAMESPACE            NAME                                         READY   STATUS    RESTARTS   AGE
kube-system          vsphere-cloud-controller-manager-8cd7k       1/1     Running   0          2m40s
kube-system          vsphere-csi-controller-55f949b89-b5spz       6/6     Running   0          2m28s
kube-system          vsphere-csi-node-27fwg                       3/3     Running   0          2m27s
vmware-system-vdo    vdo-controller-manager-6859d5c64c-h9dfh      2/2     Running   0          2m52s

kubectl get vdoconfig -A -o yaml
apiVersion: v1
items:
- apiVersion: vdo.vmware.com/v1alpha1
  kind: VDOConfig
  metadata:
    annotations:
      kubectl.kubernetes.io/last-applied-configuration: |
        {"apiVersion":"vdo.vmware.com/v1alpha1","kind":"VDOConfig","metadata":{"annotations":{},"name":"vdoconfig-sample","namespace":"vmware-system-vdo"},"spec":{"cloudProvider":{"vsphereCloudConfigs":["vspherecloudconfig-sample"]},"storageProvider":{"vsphereCloudConfig":"vspherecloudconfig-sample"}}}
    creationTimestamp: "2021-11-17T09:49:36Z"
    generation: 1
    name: vdoconfig-sample
    namespace: vmware-system-vdo
    resourceVersion: "4132"
    uid: 621714f1-c162-4206-95ac-0b6eedfa193b
  spec:
    cloudProvider:
      vsphereCloudConfigs:
      - vspherecloudconfig-sample
    storageProvider:
      vsphereCloudConfig: vspherecloudconfig-sample
  status:
    cpi:
      'nodeStatus ':
        kind-control-plane: ready
      phase: Configured
    csi:
      phase: Deployed
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.12%. Comparing base (b3e9eba) to head (5ba6060).
⚠️ Report is 29 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #99   +/-   ##
=======================================
  Coverage   52.12%   52.12%           
=======================================
  Files           6        6           
  Lines        1508     1508           
=======================================
  Hits          786      786           
  Misses        623      623           
  Partials       99       99           

Flag	Coverage Δ
unittests	52.12% <ø> (ø)

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[asifdxtreme]

LGTM

[aggarwalta]

LGTM, thanks!