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 !!

README.md

+# Description
+
+Orekit (ORbit Extrapolation KIT) is a free java library providing basic space dynamics objects and services.
+
+This repository contains examples and some additional scripts.
+
+# Licensing
+
+Orekit is licensed under the Apache License Version 2.0.
+A copy of this license is provided in the LICENSE.txt file.
+
+# Content
+
+The python-wrapper project allows using orekit in a python environment. This repository contains some key files if building the wrapper from scratch. For many applications it is recommended to use pre-built conda packages through the conda-forge python system. See the [wiki](https://gitlab.orekit.org/orekit-labs/python-wrapper/-/wikis/home) for more details.
+
+# Building from source
+
+The sources for the java classes that allows Python subclassing are no longer in a separate package but integrated in a modified orekit source fork.
+
+This fork is available at https://github.com/petrushy/Orekit
+
+A compiled jar and some other artifacts are available at https://github.com/petrushy/orekit_python_artifacts
+
+Build scripts for the automated conda package builds are at https://github.com/conda-forge/orekit-feedstock/tree/main/recipe
+
+# Support
+
+For additional support please see the [orekit forum](https://forum.orekit.org/latest)