Define how Gateways should or should not interact with GAMMA routing configuration #1478
Description
What would you like to be added:
As a followup to #1426, there is a need to clarify how traffic ingressing through a Gateway should or should not respect GAMMA routing configuration, specifically in the case when a Service specified as a backendRef of an HTTPRoute with a Gateway parentRef may have separately-configured mesh routing rules from an HTTPRoute specifying the Service as a parentRef.
An initial draft of a proposal to address this has been started in https://docs.google.com/document/d/16GZj-XFt6sAi4tMUy9Ckr99znIm6Hy0W0VeawJUdWRw/edit#
Why this is needed:
There are at least two possible approaches to handling this - expecting or allowing a Gateway to implicitly respect GAMMA routing rules (which may be difficult for Gateway API implementations focused on N/S use cases, or when mixing N/S and E/W implementations from different vendors), or requiring more explicit configuration. We should clarify the expected behavior here to facilitate GAMMA implementation.