Refactor write segmentation II (use `add_devices`)

[h-mayorquin]

A continuation of #601 and chained to it: 1) Some minor modification in the add_device function so a device is not created again if it already exists. 2) Code reduction in write_segmentation by using the add_device function. 3) Eliminate code to add the subject in the write_segmentation 4) Make the default metadata more flat in its definition.

[codecov[bot]]

Codecov Report

Merging #602 (8a78f80) into main (29b2bcf) will increase coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #602      +/-   ##
==========================================
+ Coverage   88.38%   88.42%   +0.03%     
==========================================
  Files          59       59              
  Lines        3221     3222       +1     
==========================================
+ Hits         2847     2849       +2     
+ Misses        374      373       -1     

Flag	Coverage Δ
unittests	88.42% <100.00%> (+0.03%)	:arrow_up:

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Impacted Files	Coverage Δ
...version_tools/tools/roiextractors/roiextractors.py	81.10% <100.00%> (+0.46%)	:arrow_up: