[feat] Add new action for generating dynamic Gitlab pipelines

[victorusu]

This is an initial draft of --ci-generate feature.
The feature allows for creating GitLab dynamic pipelines.

missing:

• fix overall variable names
• fix dependencies.topsort to use the _dfs function
• perform several small issues
• test in real life Gitlab CI pipelines
• add unitests, unittests and unittests!
• add documentation

Example Gitlab pipeline running the corrected deps_complex.py example: https://gitlab.com/cscs-ci/ues/reframe-ci-generate/-/pipelines/251101610

Other:

• ReFrame must be installed in the runner.

Fixes #1523.

[pep8speaks]

Hello @victorusu, Thank you for updating!

Cheers! There are no PEP8 issues in this Pull Request!Do see the ReFrame Coding Style Guide

Comment last updated at 2021-02-08 19:29:47 UTC

[victorusu]

This PR suffers from the testcase vs test dependency syndrome. 😬
Check this gist.

[codecov-io]

Codecov Report

Merging #1641 (fcf0023) into master (8dca540) will decrease coverage by 0.27%.
The diff coverage is 41.30%.

@@            Coverage Diff             @@
##           master    #1641      +/-   ##
==========================================
- Coverage   87.27%   86.99%   -0.28%     
==========================================
  Files          46       47       +1     
  Lines        7708     7751      +43     
==========================================
+ Hits         6727     6743      +16     
- Misses        981     1008      +27     

Impacted Files	Coverage Δ
reframe/frontend/ci.py	20.00% <20.00%> (ø)
reframe/frontend/cli.py	76.45% <50.00%> (-0.34%)	⬇️
reframe/frontend/dependencies.py	96.64% <100.00%> (+0.14%)	⬆️
reframe/frontend/executors/__init__.py	98.19% <100.00%> (+<0.01%)	⬆️

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[victorusu]

I tested the feature and it is working perfectly!
I liked the additional lint using the GitLab API.
I just have one comment about one sentence that has them too much. That's minor. IMHO, it could also go that way.