update user gateways to include default sa name

General MR

Summary

Ensure user specified gateways have consistent (with default public/passthrough) service account names.

Relevant logs/screenshots

Testing with values:

istioGateway:
  values:
    gateways:
      custom:
        upstream:
          labels:
            istio: ingressgateway
        gateway:
          servers:
          - hosts:
            - '*.mydomain.com'
            port:
              name: http
              number: 8080
              protocol: HTTP

Yields a consistently named service account:

Linked Issue

Closes issue

Upgrade Notices

If you are using user defined gateways, Big Bang now defaults to overriding the default service account name to use a name that is consistent with the built-in gateways (public and passthrough).

For example a custom gateway deployed with the following values would end up with a service account named custom-ingressgateway-ingressgateway-service-account where as previously the service account would have been named custom-ingressgateway

istioGateway:
  values:
    gateways:
      custom:
        upstream:
          labels:
            istio: ingressgateway

Note: No action is required unless you have a policy that utilizes the service principal based on the service account name.