protobuf: upstream_bind_config is a core.v3.BindConfig instead of an UpsteamBindConfig

*Description*:
I'm not sure if it's just "misspelt" or it has to be like this, but cluster.upstream_bind_config is a [core.v3.BindConfig](https://github.com/envoyproxy/envoy/blob/main/api/envoy/config/cluster/v3/cluster.proto#L885). I think it should be a [UpstreamBindConfig](https://github.com/envoyproxy/envoy/blob/main/api/envoy/config/cluster/v3/cluster.proto#L1073). This way UpstreameBindConfig message is totally unused. And using the current state does nothing.

*Additional questions*:
How exactly should [this](https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/cluster/v3/cluster.proto#config-cluster-v3-upstreambindconfig) field work?
With this upsteam_bind_config field should I be able to tell envoy which port_value should it use when sending datagrams to the upstream host? I mean we want to control the port value from our service gets its datagrams. Instead of letting envoy open a socket from a random port, we want to tell which specific port to use when connecting to an upstream host. Is it possible?