Integrator comparison example

[gaffarelj]

A new example should be added that shows a plot of the error in position vs the number of function evaluations for different integrators, for a pure Keplerian orbit (perturbed orbit could be added later).

The error in position from the different integrators can be computed by taking the difference w.r.t. the analytical solution of a Kepler orbit.

This example would then showcase all the different integrators available.

[gaffarelj]

This example can also be used to extract data (from the slope of the plot) to test/analyse the new integrators.

[gaffarelj]

A draft example notebook was added in tudatpy-examples/feature/integrators_example. This notebook compares the error in position for all fixed and variable step integrators implemented in tudat.