Intoduce usage agreement (issue #505)

[Raphael-Gazzotti]

Address issue #505
Correct the errors of #559

legalPerson category will need to be updated in a future PR.
the controlledTerms ModificationRights will need to be added first (openMetadataInitiative/openMINDS_controlledTerms#512).

[lzehl]

some more research and thoughts about this reveal that customUsageClause would be the better term here (because it includes permissions and reservations).

Definition for property in vocab:
Free-text usage and disclaimer information provided as part of the copyright notice. This text does not constitute a standardized license or usage agreement.

[lzehl]

sorry we need to change this back to usageCondition (because both licenses and usage agreements do not only hold permissions but also reservations). AND in principle this cannot be required (because copyright with custom usage clause could be sufficient)

[lzehl]

@Raphael-Gazzotti @apdavison @olinux @annapaola theoretically we can introduce the anyOf logic for required properties, I'm just not fully sure how:

"required": [
"accessibility",
    "fullDocumentation",
    "isVersionOf",
    "releaseDate",
    "shortName",
    "anyOf": [
      "copyright",
      "usageCondition"
     ],
     ...
  ]

?? and would this be something that the KG could interpret (and of course also then all our validation tools (e.g. in Python)

[lzehl]

NOTE: anyOf for required fields should be moved to a new issue and then introduced for v6.0 (if too complicated to fix for v5.0)