tmctl could warn users that "localhost" will refer to the container's localhost, not the machine's

[jmcx]

Many users (myself included) hit the issue of trying to access localhost from TriggerMesh components when using tmctl. Because the components run in containers, localhost does not resolve to the machine's localhost.

One idea would be for tmctl to produce a warning (non-blocking) to let the users know. Heres an idea of the message:

Warning: component <Kafka source | HTTP Poller source | ...> will run in a container, and localhost will refer to the container's localhost, not that of the host computer. 
Depending on your environment, you may need to use a special hostname like host.docker.internal (for Docker Desktop) to access the localhost. 
Some additional details are covered by [this blog post](https://www.triggermesh.com/blog/access-local-event-sources-with-tmctl-and-docker-desktop). 

[jmcx]

Maybe something in the docs?

[NikhilSharmaWe]

Hey, @jmcx when do you think we should display this warning?
Should we display it when we create a target?