I do not work for Elastic, I just volunteer on this forum, and while I agree that the documentation does not always help and it could have more examples, I don't think that this specific issue is a Elastic issue.
Basically to receive external data an agent needs to be able to listen on a port, so while configuring the agent you need to set the host as 0.0.0.0 to make it listen on all IP availables and choose any port.
For the agent it doesn't matter if you are running it on a VM, a bare metal server or a container, you just need to make sure that the external sources of data can reach that ip address and that port and this is not an Elastic issue, it is an Infrastructure and Network issue.
In this case, if you already have the agent listening on the container IP address on port 9001, then there is nothing else to configure on Elastic tools, everything else is a network/infrastructure issue.
I do not use Openshift, so I have no idea how you would configure this in Openshift, but you basically need to forward the connections to your openshift cluster to the container with the elastic agent on the specific port.