needs_id_required not supported

[danwos]

When using the src-trace directive, it creates a Src-Trace need object.
This objects gets a random id, which is not allowed if needs_id_required is set to True.
So the build stops.

Solution proposal: Allow to set ID:

.. src-trace:: example_with_file
   :id: MY_ID_005
   :project: showcase

Why is this specific need even needed?
It is not linked to traced objects nor has any metrics or other information.
And as far as I have seen, I can't configure the type of it, which may make trouble for some projects.

Updated proposal: Just remove this specific need object :)

[ubmarco]

Hehe, I came to the same conclusion in #35 (review) :)
But it might make sense to keep it in the docs (or another representation) that tells what project / folders / files were analyzed in the next section.