Add option to create animated gif

[jgieseler]

The Python package solarmach already has in the documentation an example use case that explains how to create an animated gif that consists of a set of Solar-MACH plots, see https://solarmach.readthedocs.io/en/latest/usage.html#7.1-Loop-over-multiple-datetimes-(plots). This issue is about adding an option to do this from within the streamlit version.

The question is whether this should be done totally analogous, or if it makes sense to create before a function in the solarmach Python package that is then just called from the streamlit app.

[jgieseler]

After some thought, I think it indeed makes a lot of sense to create such a function in the solarmach package. I created jgieseler/solarmach#67 for this.