Add eodag stub package

[savmickael]

When I run mypy on a code which import eodag, it claims that Skipping analyzing "eodag": module is installed, but missing library stubs or py.typed marker

It is related to this page : https://mypy.readthedocs.io/en/stable/stubs.html

So for the moment I add a type ignore in the mypy config file but it could be interesting to create the stub package for eodag

[sbrunato]

Thanks for this feature request @savmickael !