heptapod-ci: add a basic file to be able to run tests with heptapod
Having this yaml file somewhere in the main mercurial repository makes it
trivial for contributors using heptapod to run CI on their in-progress work.
There are alot of different combination (python2/python3 pure/cext/rust/pypy)
to be tested and making sure all of them are covered manually is cumbersome.
Automatic CI runnig on draft really helps in that matters. We start small bu
later changesets will add more step testing more of the variants.
The series is targetted on stable to make it available to the widest amount of contribution possible.
The definition of the docker files used for this are available here:
https://dev.heptapod.net/octobus/ci-dockerfiles
Differential Revision: https://phab.mercurial-scm.org/D8011
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).