GEP-957: Gateway port matching for Gateway API UDPRoute

[czeslavo]

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Problem Statement

Implement gateway port matching for Gateway API UDPRoute as it was defined in https://gateway-api.sigs.k8s.io/geps/gep-957/ and implemented in kubernetes-sigs/gateway-api#1002.

Proposed Solution

Check in the UDPRoute controller whether the route has been accepted by any listener and remove it from the Kong store if not.

Additional information

Blocked by #2544 (needed for proper testing of the functionality and making a single Gateway capable of serving both TCP and UDP routes).

Acceptance Criteria

• When UDPRoute's BackendObjectReference specifies a Port that doesn't match any Listener in the Gateway, it's not accepted (not in the webhook: Parser rejects it and sets an appropriate GWAPI condition)
• UDPRouteEssentials integration test is updated to cover port matching

[czeslavo]

Removing blocked label as #3325 is resolved now.