ci: add GitHub Actions next to Travis CI

[Alexis Georges]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[X] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/NationalBankBelgium/stark/blob/master/CONTRIBUTING.md#got-a-question-or-problem

Current behavior

Travis CI is unstable and we would like to replace it by GitHub Actions (See #1619)

Expected behavior

Add GitHub Actions next to Travis CI for a short period to ensure it's working well with our logic.
This first implementation does not handle release process, as it stays in Travis CI.

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?

Improve CI