Runtime configuration of HTTP fault injection per upstream cluster

*Title*: HTTP fault injection filter can have runtime settings per **downstream** cluster, but not **upstream** cluster.

*Description*:
I'm trying to simulate a failure of an external service. In my case, fault injection filter should be configured as one of the egress http filters to inject delay or abort requests to the external service.
I want to inject failure only to the requests to the specific upstream cluster (the external service) in runtime. But as described [here](https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/fault_filter#config-http-filters-fault-injection-runtime), fault injection filter allows runtime setting only per **downstream** cluster by , not **upstream** cluster.

Thanks