[stats] Add support for `track_remaining` in Circuit Breaker configuration

*Description*:
Envoy Circuit Breaker configuration supports the `track_remaining` boolean to collection of the number of resources remaining until the circuit breakers open in envoy and expose them in envoy stats. This field defaults to `false` and cannot be enabled when using Envoy Gateway.

When this field is `true`, some additional circuit breaker metrics are exposed (in prometheus, for instance)

Such metrics are extremely useful to proactively detect if a circuit breaker is about to open. Can this field be exposed in `BackendTrafficPolicy` alongside other circuit breaker settings ?

[*Relevant Links*:]
[Envoy reference for track_remaining](https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/cluster/v3/circuit_breaker.proto#envoy-v3-api-field-config-cluster-v3-circuitbreakers-thresholds-track-remaining)

[Envoy Circuit Breaker stats documentation](https://www.envoyproxy.io/docs/envoy/latest/configuration/upstream/cluster_manager/cluster_stats#config-cluster-manager-cluster-stats-circuit-breakers)