[Doc] Move (and improve) examples to docs

[RoxGamba]

We should cleanup the current examples folder (also improving the names of the files), and move/create similar example notebooks under docs/source/tutorials.

Here are some ideas:

• an example that illustrates how to download wfs from various catalogs (core, sxs, rit, iccub, gra, ...)
• an example for wf generation with teob/seob/lal
• an example for aligning waveforms
• an example for mismatches / optimizer
• an example to compute energy and linear/angular momentum from the wfs
• an example to estimate eccentricity from the wfs
• an example to calculate scattering angles from some NR or EOB data
• an example to setup twopunctures ID using EOB
• ...

Some of these have been initiated by @koustavchandra , others @SimoneA96 and @RoxGamba , @danilo-0410 should take care of.