Update helm stable repo

[oomichi]

What this PR does / why we need it:

As https://helm.sh/blog/new-location-stable-incubator-charts/ the helm stable repo is changed to https://charts.helm.sh/stable
In addition, if using helm v3.4.0+ the old stable repo installation is failed.
So this updates the stable repo to avoid such error.

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)

How Has This Been Tested?

To reproduce the issue, please run the following commands by using helm v3.4.0+

$ helm repo add stable https://kubernetes-charts.storage.googleapis.com/

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.

[aledbf]

/lgtm
/approve

[aledbf]

@oomichi thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• charts/ingress-nginx/OWNERS [aledbf]

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