This starts the rewrite of the dynamic badges. I've pulled into BaseService an initial version of the query param validation from #2325.
I've extended from BaseJsonService to avoid duplicating the deserialization logic, though it means there is a bit of duplicated code among the three dynamic services. The way to unravel this would be to move the logic from `_requestJson` and friends from the base classes into functions so DynamicJson can inherit from BaseDynamic. Would that be worth it?
This introduces a regression of #1446 for this badge.
Close#2345
There's a lot of demand for the Gitlab badges (#541) and the PR has been lingering, so I thought I'd start off one of the simple ones as a new-style service. This one is SVG-based, so it shouldn't require the API-token logic which could use some more testing and will require us to create an app and configure it on our server.
We don't have any validation in place for `queryParams`. Probably this should be added to BaseService, though for the time being I extracted a helper function.
Thanks to @LVMBDV for getting this work started in #1838!
