feat(dask): Dask integration (#600)

[Alputer]

This pull request contains the ongoing work of dask integration into REANA.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 54 lines in your changes missing coverage. Please review.

Project coverage is 75.54%. Comparing base (e36c6a2) to head (e148d06).

Files with missing lines	Patch %	Lines
reana_workflow_controller/dask.py	75.92%	39 Missing ⚠️
reana_workflow_controller/k8s.py	20.00%	8 Missing ⚠️
reana_workflow_controller/consumer.py	50.00%	4 Missing ⚠️
reana_workflow_controller/workflow_run_manager.py	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #600      +/-   ##
==========================================
- Coverage   75.59%   75.54%   -0.05%     
==========================================
  Files          15       16       +1     
  Lines        1565     1779     +214     
==========================================
+ Hits         1183     1344     +161     
- Misses        382      435      +53     

Files with missing lines	Coverage Δ
reana_workflow_controller/config.py	93.12% <100.00%> (+1.95%)	⬆️
reana_workflow_controller/workflow_run_manager.py	80.67% <57.14%> (-0.45%)	⬇️
reana_workflow_controller/consumer.py	55.27% <50.00%> (-0.28%)	⬇️
reana_workflow_controller/k8s.py	83.82% <20.00%> (-5.07%)	⬇️
reana_workflow_controller/dask.py	75.92% <75.92%> (ø)

[tiborsimko]

BTW is dashboard exposure working already? I'm getting 404 page not found when trying out locally.

[tiborsimko]

It might be good to make these hard-coded options (such as the liveness probe seconds etc) configurable via environment variables. This could come handy for some deployment scenarios. We could also do this later after the initial basic version is merged.

(Alternatively, we could think of customising the whole template, but that would surely go beyond the scope of this initial PR.)