[WIP] Adding write_derivative_description and the related test

[Remi-Gau]

I have had to write twice some code to handle writing dataset description, so I think I had better brings back #552 from the grave.

• find a better way to pass "content" to put into the description for raw and derivatives description
• find a better way to add / append pipeline information (see Adding write_derivative_description and the related test. #552 (comment))
• only update content is file already exists (should be true for raw and derivatives) with a force option to overwrite content

[codecov]

Codecov Report

Merging #811 (1af6978) into master (0f460a8) will decrease coverage by 0.20%.
The diff coverage is 60.97%.

@@            Coverage Diff             @@
##           master     #811      +/-   ##
==========================================
- Coverage   85.78%   85.57%   -0.21%     
==========================================
  Files          34       34              
  Lines        3868     3909      +41     
  Branches      994     1009      +15     
==========================================
+ Hits         3318     3345      +27     
- Misses        353      362       +9     
- Partials      197      202       +5     

Impacted Files	Coverage Δ
bids/layout/utils.py	79.74% <60.97%> (-20.26%)	⬇️
bids/layout/validation.py	80.95% <0.00%> (+2.38%)	⬆️

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[effigies]

@Remi-Gau Is this still WIP or ready for review?

[Remi-Gau]

Sorry. Still WIP