Add "Participation Model" to Benchmarking Event

[lcodo]

Specify the way participant can join to a Benchmarking Event. Options could be:

• "Under Approval" (default): data submission to these events is open to all Participant Tools, as long as the submitter is granted a "contributor" role. The petition requires to be approved by the event manager/s. Submission model Implemented
• "Open": data submission to these events is open to all Participant Tools, as long as the submitter is granted a "contributor" role. No approval is required. Submission model NOT Implemented
• "Closed": data submission to these events is restricted to set of Participant Tools selected by the event manager/s. Submission model NOT Implemented

Alternatively, we can capture in this property the anonymity requirements of the Participant Tools, i.e., "Under Approval with Identified Participant Tools", "Open with anonymous Tools", etc.

[jmfernandez]

Closed at commit bc48fa7fcba84835b36320a96976135d68220311 (please have a look both at the commit description and the schemas)