Add configuration option for the imagePullSecrets in the webhook jobs

[janosi]

What this PR does / why we need it:

The value of imagePullSecrets in the webhook patch jobs was not configurable via the values.yaml.
The default value remained the one used so far: empty list
Other appearances of the imagePullSecrets are already configurable via the values.yaml

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Which issue/s this PR fixes

How Has This Been Tested?

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added tests to cover my changes.
• All new and existing tests passed.

[k8s-ci-robot]

Hi @janosi. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[aledbf]

/ok-to-test

[aledbf]

/lgtm
/approve

[aledbf]

@janosi thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, janosi

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• charts/ingress-nginx/OWNERS [aledbf]

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