Upgrading istio to v1.18.7

[biswajit-9776]

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✏️ A brief description of the changes

I updated istio version 1.17.5 to 1.18.7

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[juliusvonkohout]

TODO:

• Update istio-cni to 1.18.7 as well
• delete the istio 1.17 folders
• fix all tests
• Update the readme
• Transform the readme into a script as we have it in /hack to upgrade synchronize istio manifests in an automated manner next time
• For istio-cni we need a script as well
• use the script to update to in several PRs to 1.19, then 1.20, then 1.21 and 1.22 for istio and istio-cni

[rimolive]

I'm not sure if the TODO items are missing work items for this PR, but if the tests passed I think we're good to move on. I'll lgtm but will hold to merge until @juliusvonkohout approves.

/lgtm
/hold

[juliusvonkohout]

TODO:

* Update istio-cni to 1.18.7 as well

* delete the istio 1.17 folders

* fix all tests

* Update the readme

* Transform the readme into a script as we have it in /hack to upgrade synchronize istio manifests in an automated manner next time

* For istio-cni we need a script as well

* use the script to update to in several PRs to 1.19, then 1.20, then 1.21 and 1.22 for istio and istio-cni

@biswajit-9776 lets continue this in a new PR then such that we can cut RC.1

[juliusvonkohout]

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: juliusvonkohout

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[juliusvonkohout]

/unhold