Describe the new feature or enhancement

We would like to add a default montage for the Artinis OctaMon fNIRS device. This would enable to have spacial locations useful for some pre-processing functions (such as the modified Beer Lamber law) and having visualization on a brain map.

Describe your proposed implementation

Adding a file in mne/channels/data/montages/, modifying set_montage() (in Raw but also other data types) as and probably the loading functions.

Additional comments

Not sure what file format is best to use (csd/sfp/txt/elc), would you have recommendations?