Modify model appending algorithm

[florent-lamiraux]

This modification follows https://github.com/stack-of-tasks/pinocchio/discussions/2203.

In the new version, when appending model B to model A on frame F, joints are copied in the following order

• joints of model A up to the parent of F,
• all the descendents of parent of F,
• the remaining joints of A.

[florent-lamiraux]

@jcarpent : I will handle your comments after fixing the tests.

[florent-lamiraux]

I addressed the above comments, modified test-cpp-model to test the new behavior, and improved the documentation of Model.supports.