Autoupdate improvements

[RebeccaMahany]

After we release the new autoupdater (#954), there are some improvements I'd like to make and new features we can add --

• TUF autoupdater should subscribe to changes in AutoupdateInterval #1412
• Embed the most recent version of root.json in our launcher binary #1705
• Report new version to K2 after update
• An "update now" functionality tied to control server: Add update-now functionality to TUF autoupdater #1579, https://github.com/kolide/k2/pull/9488
• Remove old Notary updater (Remove UseTufAutoupdater flag; always use new autoupdater #1576, Remove legacy autoupdater #1600, Deprecate notary_prefix and notary_url options #1601, Remove notary from packaging #1602, Autoupdate documentation cleanup #1572)
• Add ability to pin a particular update channel or binary version: Control server can set update channel for autoupdater #1628, Allow control server to pin version for osqueryd and launcher #1629