Migrate from istio self-managed to Managed ASM

[danisla]

Remove dependency on fixed istio releases in favor of Managed ASM release channel.

Some things to keep in mind:

• support for EnvoyFilters to preserve OPA addon support.

This will reduce the manual dependencies and deployment complexity.

[kili-ilo]

Note to self: https://cloud.google.com/service-mesh/docs/managed/service-mesh