Cluster Not Created When URLRewrite Filter Added in HTTPRoute/Rule/BackendRef

**Description:**
When a URLRewrite filter is added at the HTTPRoute/Rule/BackendRef level, Envoy Gateway does not create any cluster for that HTTPRoute, leading to 5XX.

*Example Spec*
```
spec:
rules:
- backendRefs:
- filters:
- type: URLRewrite
urlRewrite:
path:
replacePrefixMatch: /
type: ReplacePrefixMatch
group: ""
kind: Service
name: eg-validator-default
port: 8080
weight: 90
- group: ""
kind: Service
name: eg-validator-canary
port: 8080
weight: 10
```

*Observed Behavior*
No cluster is generated for this HTTPRoute when URLRewrite is applied under BackendRef.

*Expected Behavior*
Clusters should always be created, even when a URLRewrite filter is specified under BackendRef.

**Repro steps:**
- Define an HTTPRoute with a URLRewrite filter inside BackendRef.
- Apply the configuration to Envoy Gateway.
- Inspect the generated Envoy cluster configuration.
- Observe that no cluster is created for the HTTPRoute.

**Environment:**
Kubernetes Version: 1.31
Envoy Gateway Version: 1.5.0
Gateway API Version: 1.3.0