service topologies: Add service topology support to destination service

[mateiidavid]

Link to RFC

Problem Statement

Service Topology allows services to specify a topological preference as part of their spec . The preference is established based on an ordered list of labels called topologyKeys. Currently, the supported labels are:

1. kubernetes.io/hostname ⇒ route traffic of the service to endpoints on the same node/host
2. topology.kubernetes.io/zone ⇒ route traffic of the service to endpoints in the same zone
3. topology.kubernetes.io/region ⇒ route traffic of the service to endpoints in the same region
4. * ⇒ no preference

Nodes and EndpointSlices have the same labels with values set as part of their metadata. Based on the preference of the service and the origin of the traffic, a set of endpoints will be targeted. This particular issue focuses on adding support for the service labels in the endpoints_watcher part of the destination service.

Acceptance Criteria

• Handler functions in endpoints_watcher.go that target services should now also collect topologyKeys from the service spec
• servicePublisher struct which maps to a service in endpoints_watcher.go should now hold the additional topologyKeys labels in preference-order
• If the service topology feature is not active in a cluster, or if a service does not have a topologyKey field, no data should be collected/retained by the service publisher
• Unit tests should be added to the destination service to ensure topologyKeys are collected; the following files should include additional tests to ensure correct behaviour:
  1. ip_watcher_test.go
  2. endpoints_watcher_test.go

[mateiidavid]

Closed by #4780