Improve NOS client management API

Following documentation around init Connect; we identified a few improvement do to:

On com.nuxeo.connect.rest.api.CustomerResource:

• allowing to define main contact explicitly
• auto-validate org id when created with this endpoint

Plus on the current GraphQL API:

• addProject: should expose paramt about experimental/advanced features enabled?
• addProject: should as ask for project owner, and user Org main contact as project owner if missing
• addService: should correctly parse ISO dates; and not only french format: "dd/mm/YYYY"