ENH: Support named derivative paths

[tsalo]

Closes #3260.

Changes proposed in this pull request

• Copy over ToDict action from fmriprep-docker over to the main CLI parser.
• Modify the Config to handle named derivative paths.
  • E.g., --derivatives anat=/path/to/smriprep --> DatasetLinks = {'anat': '/path/to/smriprep'}
• Infer derivative name from the folder name of the derivative path if it isn't labeled.
  • E.g., --derivatives /path/to/smriprep --> DatasetLinks = {'smriprep': '/path/to/smriprep'}

[codecov]

Codecov Report

Attention: Patch coverage is 90.47619% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 73.82%. Comparing base (8eb8215) to head (cedf5bc).

❗ Current head cedf5bc differs from pull request most recent head 30a7083. Consider uploading reports for the commit 30a7083 to get more accurate results

Files	Patch %	Lines
fmriprep/workflows/base.py	0.00%	2 Missing ⚠️
fmriprep/cli/workflow.py	0.00%	1 Missing ⚠️
fmriprep/config.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3264      +/-   ##
==========================================
+ Coverage   73.62%   73.82%   +0.19%     
==========================================
  Files          56       56              
  Lines        4243     4279      +36     
==========================================
+ Hits         3124     3159      +35     
- Misses       1119     1120       +1     

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[effigies]

LGTM. Small suggestion.