[GraphHopper] Add provider parameter

[bisleadity]

Graphhopper geocoding now supports different providers. Hereby the option is given to use those providers.

As we do need to use one of those providers and there was no possibility given so far I added it.

[jbelien]

Could you maybe still add a real test? Thanks!

[bisleadity]

What's a real test for you?

[func0der]

hey @jbelien Could you elaborate on your "real test" requirement?

I would love to have this feature too.

[jbelien]

@bisleadity Sorry, I mean a test that makes a geocoding request on GraphHopper with the new provider parameter.

Thanks!