feat(config): make dask autoscaler configurable

[Alputer]

closes reanahub/reana#834

[codecov]

Codecov Report

Attention: Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 76.61%. Comparing base (1515865) to head (db9ac05).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
reana_workflow_controller/consumer.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #604      +/-   ##
==========================================
+ Coverage   76.46%   76.61%   +0.14%     
==========================================
  Files          17       17              
  Lines        1831     1847      +16     
==========================================
+ Hits         1400     1415      +15     
- Misses        431      432       +1     

Files with missing lines	Coverage Δ
reana_workflow_controller/config.py	93.95% <100.00%> (+0.08%)	⬆️
reana_workflow_controller/dask.py	76.36% <100.00%> (+1.85%)	⬆️
reana_workflow_controller/consumer.py	55.21% <33.33%> (-0.07%)	⬇️

[tiborsimko]

Cosmetics: s/dask/Dask/g in comments.

[tiborsimko]

Regarding "true" vs "True", how things work if people use uppercase or lowercase Helm values?

We may want to be ready to support two scenarios, so do some lower() gymnastics here, as we do elsewhere, for example:

os.getenv("K8S_USE_SECURITY_CONTEXT", "True").lower() == "true"

P.S. We could amend other occurrences of this boolean handling, see:

$ grep -Ei '"(true|false)' */*/config.py
reana-commons/reana_commons/config.py:    os.getenv("K8S_USE_SECURITY_CONTEXT", "True").lower() == "true"
reana-db/reana_db/config.py:    os.getenv("SQLALCHEMY_POOL_PRE_PING", "False").lower() == "true"
reana-db/reana_db/config.py:    os.getenv("REANA_PERIODIC_RESOURCE_QUOTA_UPDATE_POLICY", "false")
reana-job-controller/reana_job_controller/config.py:    strtobool(os.getenv("REANA_DB_CLOSE_POOL_CONNECTIONS", "false"))
reana-server/reana_server/config.py:DASK_ENABLED = strtobool(os.getenv("DASK_ENABLED", "true"))
reana-server/reana_server/config.py:DASK_AUTOSCALER_ENABLED = strtobool(os.getenv("DASK_AUTOSCALER_ENABLED", "true"))
reana-server/reana_server/config.py:    os.getenv("REANA_USER_EMAIL_CONFIRMATION", "true")
reana-workflow-controller/reana_workflow_controller/config.py:    {"name": "WDB_NO_BROWSER_AUTO_OPEN", "value": "True"},
reana-workflow-controller/reana_workflow_controller/config.py:    os.getenv("REANA_OPENSEARCH_ENABLED", "false").lower() == "true"
reana-workflow-controller/reana_workflow_controller/config.py:    os.getenv("REANA_OPENSEARCH_USE_SSL", "false").lower() == "true"
reana-workflow-controller/reana_workflow_controller/config.py:DASK_ENABLED = strtobool(os.getenv("DASK_ENABLED", "true"))
reana-workflow-controller/reana_workflow_controller/config.py:DASK_AUTOSCALER_ENABLED = strtobool(os.getenv("DASK_AUTOSCALER_ENABLED", "true"))
reana-workflow-engine-cwl/reana_workflow_engine_cwl/config.py:MOUNT_CVMFS = os.getenv("REANA_MOUNT_CVMFS", "false")
reana-workflow-engine-cwl/reana_workflow_engine_cwl/config.py:WORKFLOW_KERBEROS = bool(strtobool(os.getenv("REANA_WORKFLOW_KERBEROS", "false")))
reana-workflow-engine-serial/reana_workflow_engine_serial/config.py:MOUNT_CVMFS = os.getenv("REANA_MOUNT_CVMFS", "false")
reana-workflow-engine-serial/reana_workflow_engine_serial/config.py:WORKFLOW_KERBEROS = bool(strtobool(os.getenv("REANA_WORKFLOW_KERBEROS", "false")))
reana-workflow-engine-snakemake/reana_workflow_engine_snakemake/config.py:MOUNT_CVMFS = os.getenv("REANA_MOUNT_CVMFS", "false")
reana-workflow-engine-snakemake/reana_workflow_engine_snakemake/config.py:WORKFLOW_KERBEROS = bool(strtobool(os.getenv("REANA_WORKFLOW_KERBEROS", "false")))
reana-workflow-engine-yadage/reana_workflow_engine_yadage/config.py:MOUNT_CVMFS = os.getenv("REANA_MOUNT_CVMFS", "false")
reana-workflow-engine-yadage/reana_workflow_engine_yadage/config.py:WORKFLOW_KERBEROS = bool(strtobool(os.getenv("REANA_WORKFLOW_KERBEROS", "false")))