Fixing Conflicts for issue 956

See merge request !1

Fixes #956

Added method to get the measurement type.

Closes #955

See merge request !299

Added default method `getMeasurementType` in `ObservedMeasurement` that returns the name of the class
Added a constant String `MEASUREMENT_TYPE` in each measurement class to get the class name as a String
Used both additions to improve measurements type checks in tests
Fixes #955

See merge request !286

* Updated release guide with instruction for releasing a patch version
* Updated contribution guide with tips for correcting bugs planned for a patch version

Fixes #948

Add test for XML entities in NDMs

See merge request orekit/orekit!287

Updated changes.xml

Fixed these tests so Eclipse can run the tests without failing.

Add method to round a DateTimeComponents

Closes #954

See merge request orekit/orekit!297

Add constructor to AggregateBoundedPropagator

See merge request orekit/orekit!296

Added a second constructor so it can be used with a collection of
Propagator instead of BoundedPropagator. Also added a test case.

Fixes #954

Went from 254 to 253 OrekitMessages following previous commit.

Deleted unwanted modifications in this branch

Noticed that tests would run on eclipse/intellij but not with maven test. @BeforeEach methods weren't taken into account when using maven test. This was solved by adding a dependency to the junit jupiter engine as explained here : https://www.javafixing.com/2021/11/fixed-maven-does-not-run-beforeeach.html.

Deleted ExtremumApproachDetector.java and associated tests that shouldn't be in this branch.

Fixed some documentation in tests.

Changed pom to use JUnit 5 version 5.9.0.

Migrated all tests to JUnit 5.

Changed pom to use JUnit 5.

Added some documentation and improved FrameToolsTest.

getTransform(OrbitRelativeFrame fIn, FrameFacade fOut) now uses rotations instead of transforms.

Added specific test for getTransform(OrbitRelativeFrame fIn, FrameFacade fOut).

Fixed the tests so that they are similar to the Orekit philosophy.

Removed previously added dependencies such as JUnit5.

Fixed the tests so that they are similar to the Orekit philosophy.

Removed previously added dependencies such as AssertJ and JUnit5.

Added .idea/ and orekit.iml in the .gitignore

Added orekit.iml to the .gitignore file.

Added INVALID_TRANSFORM in OrekitMessages.

Fixed exception : Changed IllegalArgumentException to OrekitIllegalArgumentException.

Fixed FrameToolsTest : Deleted FrameTools-data and changed the initial orbit date so that we can use the regular-data.