Auto-install and update Cloud SDK

[chanseokoh]

Listing some tasks. There is no consistency about the granularity of the items; some may be too specific and others may be too big. There may be missing items too.

• [x] Add the feature debug flag (#2734)
• [x] Define new preferences / set initial preferences correctly (#2742)
• [x] New preference page UI (#2743)
• [x] Core install/update infrastructure (#2700 #2772 #2813)
• [x] Install at deploy
• [x] Install at local run (#2777)
• [ ] Periodic/occasional update feature when auto-managing
• [ ] Ensure updates are blocked while local run or deploy is in progress and vice versa
• [x] ~~Update notification when configured to not auto-update~~ (always updates if managed)
• [ ] Install in the background at other opportunistic times (e.g., when installing std/flex facets, Eclipse restarts, once a day, etc.) (#2801)
• [ ] Explore ways of non-blocking and atomically instant update