Allow the CLI to generate polymorphic relations

[achrinza]

This is a continuation of #2487.

At this moment, it's not possible for the LoopBack 4 CLI to generate polymorphic relations. We should update the CLI to introduce a new set of prompts for the relation generator to ask if the user wants to make the relation polymorphic, and if so, what discriminator should be used.

[j314h]

hello, is this still in progress, or has this been implemented?

[OnTheThirdDay]

This is still in progress. BTW, the polymorphic relations feature has a bug that I am working on a fix.

[j314h]

OK, thanks. thank you for your work. I think there is a problem in the documentation.
I'm testing, I'll see if there is a problem.

[OnTheThirdDay]

In case anything unclear in the doc, you can have a check of this example. https://github.com/OnTheThirdDay/lb4-polymorphic-example