[ENH] Implement variance explained threshold-based PCA option

[tsalo]

Closes #492.

Changes proposed in this pull request:

• Add an option to support a cumulative variance explained threshold-based PCA option.
• Update tests.

[codecov]

Codecov Report

Merging #658 (e76c45e) into master (dae9f20) will decrease coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #658      +/-   ##
==========================================
- Coverage   93.59%   93.48%   -0.12%     
==========================================
  Files          26       26              
  Lines        1984     2011      +27     
==========================================
+ Hits         1857     1880      +23     
- Misses        127      131       +4     

Impacted Files	Coverage Δ
tedana/decomposition/pca.py	86.36% <100.00%> (+1.74%)	⬆️
tedana/workflows/parser_utils.py	96.29% <100.00%> (+5.38%)	⬆️
tedana/workflows/tedana.py	90.44% <100.00%> (+0.03%)	⬆️
tedana/decomposition/ica.py	82.75% <0.00%> (-13.80%)	⬇️

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[eurunuela]

LGTM! Thank you @tsalo

[jbteves]

I'd like to hear your thoughts on my comments @tsalo before approving, but aside from those nitpicks this looks great, thanks!

[jbteves]

LGTM! If we end up having a demand for adding a threshold option to other PCA algorithms, we may need to create dependent CLI parameter groups. But I see no reason to cross that bridge until we get there. Thanks again @tsalo !