istio gateway should disable the automatic upstream values shift by default

Motivation

The istio/gateway chart upstream is now enforcing no additional values as of 3 weeks ago. The automatic upstream values shift breaks schema validation in that upstream chart:

 Warning  InstallFailed       100s                   helm-controller  Helm install failed for release istio-gateway/public-ingressgateway with chart gateway@1.27.1-bb.0: values do │
│ n't meet the specifications of the schema(s) in the following chart(s):                                                                                                              │
│ upstream:                                                                                                                                                                            │
│ - (root): Additional property networkPolicies is not allowed                                                                                                                         │
│ - (root): Additional property upstream is not allowed                                                                                                                                │
│ - (root): Additional property gateway is not allowed          

Acceptance Criteria

• istio-gateway's automatic passthrough values feature must be disabled