Consider CLA's as license clues?

[AyanSinhaMahapatra]

We have Contributor License agreements as licenses/rules in scancode and we should consider if we report these instead as license_clues instead of adding them in license_detections proper.

The steps discussed related to this are:

1. decide on a case by case basis if some CLA's are more like proper license detections or they are license clues.
2. if a CLA is decided as a license clue, add is_clue as True for the corresponding rules for that CLA
3. break rules containing CLA's and other proper license expressions such that all CLA rules are standalone.
4. report license matches to CLA's in license_clues

We also have detections of CLAs here in the license report contributed by Porsche AG OSO w.r.t discussion in ORT community meeting on scancode false positives.

Also see #2877 for the discussion of adding is_clue flag to rules, w.r.t different cases.

These are some CLAs in scancode licenses:

(Have to decide which of these are clues or not)

is_clue	license_key	short_name	name
True	dco-1.1	DCO 1.1	Developer Certificate of Origin 1.1
True	dgraph-cla	Dgraph Community License Agreement	Dgraph Community License Agreement
True	generic-cla	Generic CLA	Prior Generic Contributor License Agreement
True	isotope-cla	Isotope Commercial License Agreement	Isotope Commercial License Agreement
True	jetty-ccla-1.1	Jetty CCLA 1.1	Jetty Project Corporate Contributor License Agreement V1.1
True	newton-king-cla	Newton-King CLA	James Newton-King CLA
True	owf-cla-1.0-copyright-patent	OWF CLA 1.0 - Copyright and Patent	OWF Contributor License Agreement 1.0 - Copyright and Patent
True	owf-cla-1.0-copyright	OWF CLA 1.0 - Copyright	OWF Contributor License Agreement 1.0 - Copyright

[DennisClark]

Most of these items are not really software "licenses" but Contributor License Agreements (CLA's) that describe the allowed or required licensing that any contributor should assign to a code contribution. There are two items in the list that are not CLA's but rather proper licenses:

dgraph-cla | Dgraph Community License Agreement
is a "Source-available" license (note that this category is not open source).

isotope-cla | Isotope Commercial License Agreement
is a "Commercial" license.

So the other items are certainly important useful information (basically "key files" or "notices") about a software project, but do not really identify the license-expression that should apply to that project. @AyanSinhaMahapatra I will let you and @pombredanne determine the best way to handle them; your proposed solution looks fine to me.

[DennisClark]

we are now treating CLA's as another category of license and we return them in license expressions