and add Python 3.12 compat explicitly

- use official Python Debian docker images instead of custom images
- jdk4py is now used instead of installing openjdk on linux
- A matrix of several Python versions (3.9 to 3.12) is used for testing
- add build stage which tries building the python wheel (available for one day as an artifact)
- add flake8 step in test stage to lint the code and produce a code quality report (available as an artifact)
- the test step now also computes the test coverage (available as an artifact)

for instance from jdk4py, without having to use a JAVA_HOME environment variable

- test orekit_converters.py
- test pyhelpers.py
- test orekit_jpype.py
The tests that start the JVM are split into several files meant to be run separately because the JVM cannot be restarted (known jpype/JNI limitation)

- Maven allows downloading JARs (it now only requires changing the Orekit or Hipparchus or Rugged version in pom.xml)
- Javadoc JARs are only required for generating stubs, so they don't need to be packaged. This reduces the wheel size by more than half

add CI pipeline

See merge request Petrush/orekit_jpype!8

add hook to make orekit_jpype pyinstallable

See merge request Petrush/orekit_jpype!6

 using a docker image from the ci-utils repo ci-utils!3

I had an error complaining that numpy was not found, and is needed for the helper functions which convert arrays.

Heavily inspired from https://github.com/jpype-project/jpype/pull/877

Custom jars support

See merge request Petrush/orekit_jpype!7

Additional tests

See merge request Petrush/orekit_jpype!5

Automatically convert java strings to python strings (as in JCC version)

See merge request Petrush/orekit_jpype!4