feature: Add support to opt-out from zone aware routing via Ingress/RouteGroup

[greeshma1196]

Introduce the annotation zalando.org/traffic-zone-aware: "false" on Ingress and RouteGroup resources. When set, the resource receives all endpoints across all zones, bypassing zone filtering both at the dataclient layer (endpoint fetch) and at the routesrv layer (per-zone route serving).

Usage:

metadata:
  annotations:
    zalando.org/traffic-zone-aware: "false"

Tasks

1. Define zalando.org/traffic-zone-aware annotation constant in the kubernetes package
2. Extend eskip.Route with EnableZoneAwareness field to carry the annotation value through the route pipeline to routesrv
3. Modify GetEndpointSlicesByService and GetEndpointSlicesByTarget in clusterstate.go to accept zoneAwareTraffic param and skip zone filtering when value is "false"
4. Modify Ingress v1 path rule conversion (convertPathRuleV1) and default backend conversion (convertDefaultBackendV1) to read the annotation, pass it to endpoint fetch, and set r.EnableZoneAwareness
5. Modify RouteGroup backend application (applyServiceBackend) to read the annotation, pass it to endpoint fetch, and set r.EnableZoneAwareness
6. Modify getRouteForZone in routesrv/polling.go to return the route unmodified when EnableZoneAwareness == "false"
7. Add integration test with two Ingresses in zone eu-central-1a: one opted out (expects all endpoints across zones), one default (expects only zone-local endpoints)
8. Add unit tests for filterRoutesByZone covering opt-out scenarios: both routes opted out, opt-out mixed with normal route, and opt-out with a below-threshold zone

ref: #3971

[szuecs]

I don't think it's a good idea to have it in eskip.
It has nothing to do with the language.

[szuecs]

In general I think we might want to pass the new filter through the ingress context and routegroup context instead of a parameter of a function. The parameter feels disconnected to the other.

[greeshma1196]

@szuecs If we pass the annotation through ingress/routegroup context, RouteSRV still needs to know whether to filter this route or not. In order for that to work we need to set a field within the Route struct.
But maybe if it is a filter we can reference route.Filters to check if the disableZoneAwareness() is set. What do you think?