A basic conduit init command

[hariso]

The purpose of this command is to provide a better onboarding experience.

This should be a basic command that makes it possible to:

• create a demo pipeline with conduit init
• create a pipeline with a given source, destination, and possibly a processor, e.g. conduit init --source SRC_PLUGIN --destination DEST_PLUGIN --processor PROC_PLUGIN

This version is not part of #1911 and some parts of it will be rewritten to use the new CLI code. The logic (that generates a pipeline given a source, destination, etc.) should be re-usable.