chore(yamllint): add and integrate yamllint

2 jobs for !13 with topic/default/yamllint in 38 seconds (queued for 10 seconds)
latest merge request
Name Stage Failure
failed
py27 Tests
WARNING: You are using pip version 20.0.2; however, version 20.3.4 is available.
You should consider upgrading via the '/builds/cubicweb/cubes/email/.tox/py27/bin/python -m pip install --upgrade pip' command.

=================================== log end ====================================
ERROR: could not install deps [-rrequirements-test.txt]; v = InvocationError(u'/builds/cubicweb/cubes/email/.tox/py27/bin/python -m pip install -rrequirements-test.txt', 1)
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ERROR: py27: could not install deps [-rrequirements-test.txt]; v = InvocationError(u'/builds/cubicweb/cubes/email/.tox/py27/bin/python -m pip install -rrequirements-test.txt', 1)
Cleaning up file based variables
ERROR: Job failed: command terminated with exit code 1