Add option to hide LHS sidebar stats

I don't really use them, and they take valuable vertical space which becomes annoying when you're in many teams and have to scroll the list of team buttons. It's worse when you're connected to both GitLab and GitHub, since now you easily lose almost 25% of your vertical space to these plugins.

Of course I could use a selector in my ad blocker to hide it, but a setting for it would be much cleaner!

Start by locating the LHS sidebar stats rendering and the plugin's user-facing settings entry point. Add a setting that controls whether those stats are shown, and verify that hiding them restores vertical space for the team buttons without affecting the rest of the sidebar.

Written by the indexing model from the issue text.