feat: request UPF to allocate F-TEID

[gruyaume]

Description

As of 3GPP release 16, the F-TEID should be allocated by the UPF (and not by the SMF). Here we make the necessary changes for the SMF to request the UPF to allocate the F-TEID through PFCP and we remove the F-TEID allocation from the SMF.

⚠️ Warning: This is a breaking change. This PR goes hand in hand with the change in the UPF.

Context

From the 3GPP specification referenced below:

For EPC and 5GC, F-TEID shall be only allocated by the UP function, see clause 5.8.2.3 of 3GPP TS 23.501[28].
The UP function shall set the FTUP feature flag in the UP Function Features IE (see clause 8.2.25) and the CP function
shall request the UP function to allocate the F-TEID. The UP function shall reject a request to establish a new PDR with
an F-TEID allocation in the CP function option, with the cause "Invalid F-TEID allocation option". As an exception, the
UP Function shall accept the PFCP Session Establishment Request message with a PDR including an existing F-TEID
to re-establish a PFCP session during a restoration procedure as specified in clause 4.3.2 of 3GPP TS 23.527 [40] and
clauses 16.1A.4 and 17.1A.4 of 3GPP TS 23.007 [24].

Reference

• https://www.etsi.org/deliver/etsi_ts/129200_129299/129244/16.05.00_60/ts_129244v160500p.pdf
• feat: add F-TEID allocation support upf#840

[thakurajayL]

Not reviewing since its in draft state !