Add `section` property to action

[TNorbury]

Discussed in https://github.com/TNorbury/command_palette/discussions/15

^{Originally posted by karniv00l July 6, 2022} Hi 👋

I think it would be nice to be able to categorize actions with something like a section. Like in kbar.

Example:

[romanr]

Yes, especially if you use command palette for commands and search, which always the case, it needs visual separation of commands and data search results.