Add RM Requirement validation on POST/PUT using lyo-validation

[berezovskyi]

For example, to enforce @OslcOccurs(Occurs.ExactlyOne) on oslc_rm:Requirement. Main aim is to make use of lyo-validation.

The code should be quite straightforward:

https://github.com/eclipse/lyo/blob/c8cf9a4f899e1a094a57b2d776ceaaa30d33c285/validation/src/test/java/org/eclipse/lyo/validation/ValidationExample.java#L110-L111