[auto-bump][chart] istio-1.9.1

[d2iq-dispatch]

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]

This repo has @mesosphere-mergebot integration. You can perform the following commands by submitting a comment. Submit a comment with content "@mesosphere-mergebot help" to view more detailed help text and examples. Be sure the have a look at the mergebot documentation, too.

@mesosphere-mergebot backport  

[joejulian]

@mesosphere-mergebot backport release/4

[d2iq-mergebot]

Backport PR for release/4: #1021