Unpin xarray version

[LukeWeidenwalker]

@ValentinaHutter Is there a specific reason why xarray is pinned to 0.18.2? Unpinning this would make installation on dask-gateway much easier!

[soxofaan]

FYI: About pinned dependencies: this blog post was enlightening to me back in the time when I was struggling with the same question. Short version:

• applications (software you deploy) should have their dependencies pinned down in requirements.txt (or something equivalent)
• libraries (software you package to be reused/redistributed in other applications and environments, like openeo-processes-python) should have abstract, liberally constrained dependencies in setup.py/setup.cfg. And with liberally constrained I mean something like foo>=1.2.3: we need at least version 1.2.3 of library foo and anything above that should work too

[LukeWeidenwalker]

Thanks, this is very helpful, that's a clear way to think about it - I think I will start linking to that article myself! ;)

In that spirit I'll update to xarray>=0.18.2 - this is still a bit arbitrary, but it's the lowest version we know that this library works with for sure. Our backend applications that use this library have their versions pinned anyways, so this shouldn't break anything.