gateway API future work

[illume]

This is a list of future work items left over from the original gateway API PR:

• experimental features
• Testing with a service mesh, and mesh related gateway functionality
• add better http route rule UX (filters, backends,...)
• add tls UX to gateway
• add gateway api to map feature
• visualization (there's some existing tools to visualize these)
• do not loop forever when message when Gateway API is not available #2738

The original gateway API PR:

• frontend: add support for gateway-api #2504