Investigate and eventually implement missing steps of Figure 4.3.4.2-1 3GPP TS 23.502, _UE or network requested PDU Session Release for Non-Roaming and Roaming with Local Breakout_, or Figure 4.3.4.3-1: _UE or network requested PDU Session Release for home-routed roaming:_ Both are triggered by NAS PDU Session Release Request, which is not implemented. To be investigated whether other messages and/or API are possibly missing. * UE-side NAS PDU Session Release Request encoding, callback, unit tests * UE-side NAS PDU Session Release Ack encoding, callback, unit tests * UE-side: review NAS exchange between UE and network (steps 4,5,6 - forwarding might be incomplete) * CN-side: verify implementation of the message in the CN - are they all done? was UE initiated PDU session release in these scenarios validated with COTS UE? * Testing and validation   See thread: [3684#note_190094](https://gitlab.eurecom.fr/oai/openairinterface5g/-/merge_requests/3684#note_190094)