JupyterViz: Allow user to specify space figure output format in svg/png & savefig kwargs

[rht]

Currently, it is hardcoded to be png, because png is much faster. According to #1819 (comment), we should allow user to pass in extra arguments to solara.FigureMatplotlib. According to https://solara.dev/api/matplotlib, the kwargs is for extra arguments to Matplotlib's savefig, i.e. Solara renders a figure by doing a savefig operation.

cc: @ankitk50. This doesn't require agreement/consensus on the design of how this is going to implemented, and so there shouldn't be any blocker.