CLI option to render specific section within scene for development workflow

[marcel-goldschen-ohm]

Description of proposed feature

For development workflows and UI integration, it would be useful to be able to specify in the render command a specific section within a scene to render. For example, something like

manim myfile.py MyScene:3

would render only the 4th section of MyScene (the equivalent to setting skip_animations=True for all sections except the 4th in MyScene).

Currently, this can be done by manually setting the skip_animations argument in each call to self.next_section(...). However, it would be much more convenient to be able to indicate which subsection to animate separate from the scene code. This would also make it much simpler to implement this sort of development workflow in UIs which at the moment would have to programmatically edit the code file to achieve this simple and likely widely used development paradigm.