Unknown/no Info Surgical Procedure

[gcangioli]

make explicit how to manage the case of unknown surgical procedures.

• [ ] add this case in the model mapping
• [ ] add the unknown concept to the value set used for the procedure.code

[gcangioli]

implemented in https://github.com/hl7-eu/pcsp/commit/b579d8d9c983362f6c2f6b3bccac8f067ba031fe