Jetpack Checklist: Start installation if not started yet

If for some reason we buy a plan for Jetpack and don't set VP/AK for it, and try to access http://calypso.localhost:3000/plans/my-plan/:site - it will appear that they're being installed right now, but they really aren't.

Let's make sure we trigger the installation if that page is accessed and we consider that one of the plugins still needs to be installed.

To make this work, we'll need to check the current installation progress, and if it's not `100%`, hook up the `` component to start the install.

Reported by @seear in https://github.com/Automattic/wp-calypso/pull/32279#issuecomment-483661895.

Start at the /plans/my-plan/:site page and trace how the component receives current installation progress. Reproduce the case where a plan has no VP/AK and progress is below 100%, then verify that opening the page starts installation and that already-complete installations are unchanged.

Written by the indexing model from the issue text.