Upgrade istio to v1.20.6

[biswajit-9776]

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✏️ A brief description of the changes

I updated istio from version 1.19.10 to 1.20.6

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[biswajit-9776]

The scripts are not fully optimal and I might work on them at end of v1.22.0.

[juliusvonkohout]

Yes, the scripts should be closer to the other ones.

/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: juliusvonkohout

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