Remove shared auth policies for Keycloak

General MR

Summary

This work is part of the Istio Authorization Policies Clean Up epic, for BB issue #2028:

• Removed shared authorization policies that got moved to the istio-system namespace.

• Removed all references to Values.istio.hardened in tests/test-values.yaml as they can't run in the package pipelines.

• Updated /docs/IstioHardened.md to point to the Big Bang IstioHardened.md.

• Updated the path for the authorization policies to /chart/templates/bigbang/istio/authorizationPolicies.

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