Update Python API

[CasperWA]

Part 1 of closing #95.

Update the Python API; split out the individual task functions to separate files/modules, where task-specific utility functions can be added as well.

This only "true" changes here belongs to the last commit; fc56da1, which ensures fail_fast works as intended. This was necessary to satisfy mypy (and also fix that issue, really).

Note, this is part 1 of 3 of a new set of PRs that replace #99.

Closes #112

[codecov-commenter]

Codecov Report

Merging #109 (2046157) into main (2e0929c) will increase coverage by 3.91%.
The diff coverage is 57.74%.

@@            Coverage Diff             @@
##             main     #109      +/-   ##
==========================================
+ Coverage   53.69%   57.61%   +3.91%     
==========================================
  Files           3        8       +5     
  Lines         311      361      +50     
==========================================
+ Hits          167      208      +41     
- Misses        144      153       +9     

Impacted Files	Coverage Δ
ci_cd/tasks/docs_index.py	23.33% <23.33%> (ø)
ci_cd/tasks/setver.py	23.52% <23.52%> (ø)
ci_cd/tasks/api_reference_docs.py	65.41% <65.41%> (ø)
ci_cd/tasks/update_deps.py	68.81% <68.81%> (ø)
ci_cd/utils.py	69.76% <69.76%> (ø)
ci_cd/tasks/__init__.py	100.00% <100.00%> (ø)

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[francescalb]

Looks fine