syncNow debouncing should be configurable from the client call site.

[MatthewTighe]

With the increased focus on FxA accounts, it would make sense for a call to syncNow to be able to specify its debounce window. For example, a specific syncNow call might want to debounce to 5 or 30 seconds, rather than the full 5 minutes that is the current default.

Assuming this is completed after #12645, then there could be debounced timers tracked for individual engines as well. For example, we may want to sync tabs every 5 seconds but only need to sync bookmarks every minute at most. Full syncs could be debounced if any engine is outside the specified debounce window.

┆Issue is synchronized with this Jira Task

[jonalmeida]

Moved to bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1794222

Change performed by the Move to Bugzilla add-on.

[rocketsroger]

Notes:
Investigation into if we should persist debounce time for each engine.
Update debounce time for each engine on sync success.