Provide a well defined terminlogy to encode label meaning semantically

[rfloca]

Currently MONAI Label just encodes/provides labels by their names (and potentially the pixel values).
There is no well defined set of codes provided to really encode (if possible) the meaning and semantics of a label. That makes it harder to robustly integrate/deploy models that are provided by MONAI Label.
Basic Idea:
MONAI Label should provide as pragmatic light weighted way to use a dictionary that not just encodes a human readable name for a label, but also additional semantic encodings (e.g. based on SNOMEDCT or DICOM) that allows to encode e.g. the anatomic region, primary anatomic structures or other properties.
Integrating/wrapping a model for MONAI Label would also then mean to make that mapping, if possible, to ensure that the results provided by a model are as rich encoded as possible.
(Thought: May be also the fact if a model supports this rich well-defined encoding or not should directly be query-able via the REST API, as it might be an important decision for host application, if they want to offer it)
There are already works out there in that direction (e.g. 3DSlicer, MITK, EUCAIM). We should check the SotA and see if we can just rely on something or a new community standard/dictionary should be established.

First Steps:

• SotA analysis
• Specify how we propose to encode
• Design concept for how to integrate it into the REST API, dev workflows etc. and implementation plan (smaller tangible issues)

[pieper]

This is a great idea 👍

For reference, here's the way we approach this in Slicer (based on SNOMED and DICOM): https://slicer.readthedocs.io/en/latest/user_guide/modules/terminologies.html