Forward ambient mode to wrapper

Summary

• forward istio.ambient.enabled through wrapper Big Bang values
• retain istio.enabled passdown
• add wrapper values Secret coverage

Related Merge Request

wrapper !63: Add wrapper deprecation and ambient-mode warnings

Linked Issue

Closes #3374 (closed)

Upgrade Notices

N/A

Validation

• PATH="/opt/homebrew/bin:$PATH" helm unittest chart -f 'unittests/**/*_test.yaml' (64 suites, 358 tests passed)
• helm lint chart
• rendered a wrapper-enabled package and verified bigbang.istio.ambient.enabled: true