add helm parameter imagePullSecrets

[huiwq1990]

What this PR does / why we need it:

This PR aims to implement this feature: https://kubernetes.io/docs/tasks/configure-pod-container/pull-image-private-registry/ , allow use set private registry credentials. Demo shows below:

controllermanager:
  imagePullSecrets:
    - name: my-sercret
  controller:
    repository: private.registry.local
  webhook:
    repository: private.registry.local

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

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[xunpan]

@huiwq1990
thanks for your contribution. Please sign CLA first.

[hectorj2f]

@huiwq1990 Please, update the README to add the new property.

[hectorj2f]

/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hectorj2f, huiwq1990

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