Resolve "Add background susbtraction to HCI pipeline?"
Closes #158 (closed)
Also updates many of the figures such that the boxes show an enumeration of the concrete dataitems instead of the abstract ones.
Associated DRLD MR: https://gitlab.astro-wise.org/micado/datareductionlibrarydesigndrs/-/merge_requests/88
Code in create_associationmatrix.py
got a bit more ugly and should be refactored some day.