Support loading orekit data from Python library

The support for downloading the Orekit data repo as a Python library using pip was introduced in orekit/orekit-data!4 (merged)

This merge request mostly adds an option to the setup_orekit_cur method to try loading the data from the orekitdata library. This option defaults to False to not break compatibility with existing code. If the orekitdata import fails, the method will continue searching for orekitdata using the filename argument, as before.

TODO after merge of orekit/orekit-data!4 (merged) : replace the URL https://gitlab.orekit.org/yzokras/orekit-data.git by https://gitlab.orekit.org/orekit/orekit-data.git !!