[Orekit Developers] switching to Hipparchus 1.2

[MAISONOBE Luc <luc.maisonobe@c-s.fr>]

Hi all,

Version 1.2 of the Hipparchus mathematical library has just been released.
This version includes fixes that are important for Orekit (the one
concerning <https://github.com/Hipparchus-Math/hipparchus/issues/23>
was initially identified using Orekit ellipsoid tesselation) and
improvements thtat Orekit can use (introduction of Tuple fields).

I will therefore change Orekit dependency to Hipparchus 1.2 for
the upcoming Orekit 9.1 release. The change will be done on the
Orekit pom.xml file in a few minutes. A new test case using the
Tuple field for multi-satellite propagation will be set up that
mandates use of Hipparchus 1.2. So users doing nightly builds
will need to updte their configuration.

best regards,
Luc