Reduce frequency of the browser extension SiteProductVersion query

Created by: Joelkw

This currently hits our api 120 times/second. It dwarfs all other queries, by far.

It's not urgent, since it doesn't hit the database, but we should figure out a cleaner solution.

From @marekweb:

This feature originated in RFC 221 to help users who may be logged-out from their instance and not know about it. The only thing that this feature does is that is adds a red indicator to the browser extension's toolbar action item, to encourage the user to open the options menu and see what's wrong. A better implementation would watch for 401 responses from normally occurring requests and avoid querying this endpoint entirely, except when validating the URL when it's updated by the user.

Originally here (but copied important context over to this issue).