deprecations setuptools

[mdonadoni]

• ci(pytest): invoke pytest directly instead of setup.py test (deprecations setuptools #459)
• build(python): remove deprecated pytest-runner (deprecations setuptools #459)
• build(python): use optional dependencies instead of tests_require (deprecations setuptools #459)
• build(python): add minimal pyproject.toml (deprecations setuptools #459)
• build(docker): pin setuptools to v70 (deprecations setuptools #459)

Closes reanahub/reana#814

[wirespecter]

Looks good :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 45.99%. Comparing base (20899e7) to head (1288088).
Report is 14 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #459   +/-   ##
=======================================
  Coverage   45.99%   45.99%           
=======================================
  Files          17       17           
  Lines        1235     1235           
=======================================
  Hits          568      568           
  Misses        667      667