DOC: convert notebooks to .rst files in the documentation

[Gui-FernandesBR]

Is your feature request related to a problem? Please describe.

We have been using jupyter notebooks to create documentation pages for rocketpy since many years ago.
A more modern way to do that is keeping .rst files, which are more customizable and allow for a better visualization in general.

Describe the solution you'd like

• In the docs folder, convert the .ipynb to .rst (see nbconvert)
• OPTIONAL: create a folder with "dev" scripts to be used for developers when trying to test new features.

Additional context

Be careful if you set all the simulations to be run during the docs building process, that could slow down the whole thing excessively.