[release/4][BACKPORT] [auto-bump][chart] istio-1.9.1

[d2iq-mergebot]

This is a backport of the following PR:

#983

What type of PR is this?
Chore

What this PR does/ why we need it:
Bumps istio to the latest version

Which issue(s) this PR fixes:
no issue

Special notes for your reviewer:
Manually did the upgrade testing by spinning up a konvoy 1.7.1 cluster with istio enabled and then used this chart to upgrade istio to 1.9.1. Verified that the applications that were running prior to upgrade continued to run after upgrade as well.

Does this PR introduce a user-facing change?:

istio version upgraded to 1.9.1

Checklist

• If a chart is changed, the chart version is correctly incremented.
• The commit message explains the changes and why are needed.
• The code builds and passes lint/style checks locally.
• The relevant subset of integration tests pass locally.
• The core changes are covered by tests.
• The documentation is updated where needed.

[d2iq-mergebot]

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@mesosphere-mergebot backport  

[joejulian]

Admin merging as this was manually tested and the CI job doesn't correctly determine versions from the targetted repo.