Docs: Update docs to reflect santasyncservice

[russellhancox]

There is a list of binaries in the "Binaries" section of the documentation but it's missing santasyncservice (and santametricservice). This should be added, and the "Syncing Overview" page should also be updated to reflect that santasyncservice is now responsible for syncing and is managed by launchd instead of being directly launched by santad.