Add support for GatewayAPI's UDPRoute

[abaguas]

This PR is the third of a series implementing support for the GatewayAPI: #954

This PR adds support for UDPRoute resources. The implementation is the exact same as for TCPRoute resources (#2116):

apiVersion: gateway.networking.k8s.io/v1alpha2
kind: UDPRoute
metadata:
  name: gatewayapi-udproute
  namespace: test-gslb
spec:
  parentRefs:
  - name: gatewayapi-gateway
  rules:
  - backendRefs:
    - name: gatewayapi-udproute-service
      port: 8080

Similarly to TCPRoute resources, the UDPRoute does not have a hostname, therefore we rely on the GSLB's k8gb.io/hostname annotation to fetch it. We also do this for services of type load balancer:

apiVersion: k8gb.absa.oss/v1beta1
kind: Gslb
metadata:
  name: gatewayapi-udproute
  namespace: test-gslb
  labels:
    k8gb.io/hostname: gatewayapi-udproute.cloud.example.com
spec:
  resourceRef:
    apiVersion: gateway.networking.k8s.io/v1alpha2
    kind: TCPRoute
    name: gatewayapi-udproute
  strategy:
    type: roundRobin
    dnsTtlSeconds: 30

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[ytsarev]

Rebased, added udp route to local setup, fixed annotation, tested failover end-to-end.