Support Ring Hash Load Balancing Policy in BackendTrafficPolicy

*Description*:
> Currently, when configuring consistent hashing via BackendTrafficPolicy, Envoy Gateway defaults the underlying Envoy load balancing policy to Maglev. While Maglev is efficient for large lookups, it lacks some of the configuration flexibility and specific stability characteristics provided by Ring Hash, which is natively supported by the Envoy proxy.
To achieve Ring Hash today, users must resort to EnvoyPatchPolicy (xDS patching), which is complex to maintain and requires manual cluster name targeting. It would be beneficial to have RingHash as a first-class option within the BackendTrafficPolicy API.

Current Behavior
Setting loadBalancer.type: ConsistentHash in a BackendTrafficPolicy automatically generates an Envoy Cluster with lb_policy: MAGLEV. There is no field to specify an alternative consistent hashing algorithm.

Proposed Enhancement
Extend the BackendTrafficPolicy (or the loadBalancer configuration) to allow users to specify the consistent hashing algorithm and its associated parameters.
Example:
```
spec:
loadBalancer:
type: ConsistentHash
consistentHash:
type: Header
header:
name: x-user-id
lbPolicy: RingHash

```