WIP: Added changes for AFP PEB (ATR-23946)

Following the idea of having AFP as an additionnal PEB stream (see https://its.cern.ch/jira/browse/ATR-23946), here's the corresponding WIP MR that enables AFP to be written out as a subdetector on its own.

This is here to be cross-checked by @rbielski for correctness of PEB syntax rather than to be merged. Before merging it, we need to complete this MR (!44305 (closed)) as it will contain relevant TLA/PEB changes. Once that MR is in, we will update this one with the new reference files as well.