Provide the same functionality in mesh gateway policies as traffic routing policies

We are asking to add the same functionality in MeshGatewayRoute as exists in TrafficRoute. Not all features of the TrafficRoute (https://kuma.io/docs/1.7.x/policies/traffic-route/#usage) policy is supported by the mesh gateway MeshGatewayRoute (https://kuma.io/docs/1.7.x/policies/mesh-gateway-route/). For example we would need: request and response modification and load balancing.