Configurable image pull secrets in Helm charts

[saileshd1402]

What this PR does / why we need it:
This PR adds configurable images pull secrets for kserve controller and serving runtimes from Helm charts.

Currently, to add image pull secrets for images in Helm installations, we will have to patch the secrets after deploying the helm charts. With this change we can add it through the Helm command itself.

Example of configuring image pull secrets for kserve controller:

helm install kserve charts/kserve-resources/ --set kserve.controller.imagePullSecrets[0].name=kserve-controller-secret

Example of configuring image pull secrets for cluster serving runtime (huggingfaceserver):

helm install kserve charts/kserve-resources/ --set kserve.servingruntime.huggingfaceserver.imagePullSecrets[0].name=huggingface-secret

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 #

Type of changes
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• New feature (non-breaking change which adds functionality)

Feature/Issue validation/testing:

Please describe the tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
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• Test A

• Test B

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Special notes for your reviewer:

1. Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

Checklist:

• Have you added unit/e2e tests that prove your fix is effective or that this feature works?
• Has code been commented, particularly in hard-to-understand areas?
• Have you made corresponding changes to the documentation?

Release note:

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[saileshd1402]

Hi @yuzisun, I wanted your thoughts on this PR. We think it'll helpful during helm installations for image pull secrets to be customisable. I think this PR is ready for review, please let me know if there are any other changes to be made.

[saileshd1402]

Hi, @terrytangyuan, I wanted your thoughts on this PR, and if you think any changes are necessary.
cc: @johnugeorge

[yuzisun]

/lgtm
/approve