Add GitLab CI template

Thanks for working on this one @ptmkenny. It looks like that the tests need to be updated to be compatible with the latest changes in Feeds. The tests of Feeds Extensible Parsers always run on top of the dev version of Feeds. This is done this way to detect if changes in Feeds would accidentally break Feeds Extensible Parsers, but also for cases where a new feature of Feeds is added and I'd like to adapt Feeds Extensible Parsers based on that new feature.

@MegaChriz Happy to help. I will look into fixing the tests, but do you want that as part of this MR or should it be a separate MR? (I'm inclined to put it in a separate MR, since this issue is about the testing framework, not the tests themselves.) But I can also understand you might want tests to pass on every commit.

Ok, the fix was simple enough so I already made another issue here: 🐛 Fix tests to match latest version of Feeds Needs review

Alright, I'll merge this and the other one then. 🙂

Automatically closed - issue fixed for 2 weeks with no activity.