Updating overview.md to include verbiage on Istio hardening
General MR
Summary
This MR references the package addition for Istio hardening, Ref MR, that will cause breaking changes if Istio hardening is enabled for Twistlock.
The internal configuration for cloud providers and secret stores will be block until a customServiceEntry is added for the required external services. That configuration is too extensive and service specific to add at the package level and should be determined by the end user and added to their Big Bang overrides or their Big Bang values.yaml. The overview.md has been updated to acknowledge this change with reference to IstioHardened.md as well as an AWS example.
Relevant logs/screenshots
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Linked Issue
Upgrade Notices
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