Create chapter that demonstrates Lagrange's approach to constrained systems

[moorepants]

We've agreed to add this as a lesson in the 2023 course, so we need a chapter to go along with it. Probably should go after the DAE simulation chapter so that we can apply the DAE integrator to this system.

[wwolfie]

Linking the (currently draft) pull request:

https://github.com/moorepants/learn-multibody-dynamics/pull/140

[moorepants]

Done!