WIP Add metadata propagation

[bogdang989]

Follow-up for common-workflow-language/common-workflow-language#710

[tetron]

This is cool. I owe you a code review.

[codecov[bot]]

Codecov Report

Merging #876 into master will increase coverage by 0.98%. The diff coverage is 10.34%.

@@            Coverage Diff            @@
##           master    #876      +/-   ##
=========================================
+ Coverage   72.71%   73.7%   +0.98%     
=========================================
  Files          29      33       +4     
  Lines        5810    6462     +652     
  Branches     1454    1637     +183     
=========================================
+ Hits         4225    4763     +538     
- Misses       1133    1244     +111     
- Partials      452     455       +3

Impacted Files	Coverage Δ
cwltool/builder.py	80% <100%> (+16.36%)	:arrow_up:
cwltool/command_line_tool.py	83.65% <7.14%> (+4.18%)	:arrow_up:
cwltool/docker_id.py	47.91% <0%> (-2.09%)	:arrow_down:
cwltool/context.py	96.46% <0%> (-0.87%)	:arrow_down:
cwltool/flatten.py	78.94% <0%> (ø)
cwltool/__init__.py	100% <0%> (ø)
cwltool/main.py	32.5% <0%> (ø)
cwltool/utils.py	53.44% <0%> (ø)
cwltool/argparser.py	83.88% <0%> (+0.47%)	:arrow_up:
cwltool/executors.py	76.79% <0%> (+2.2%)	:arrow_up:
... and 13 more

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