[Performance] Notes sync should only be performed after a set amount of time or a few seconds after the writing stops

[SoftVision-PaulOiegas]

[Affected versions]:

• Firefox 61.0.1 and above

[Affected Platforms]:

• Desktop & Mobile

[Prerequisites]:

• Have the latest Notes Desktop installed on a new profile
• You are already signed in with a Firefox Account.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Click the "+ New Note" button to create a new note.
3. Write one character and observe the sync functionality behavior.
4. Write another character and observe again the sync behavior.

[Expected result]:

• For performance reasons, sync is only performed after a set amount of time (eg: 1 minute), or after a few seconds after the writing stops (eg: 10 seconds).

[Actual result]:

• Sync is performed after each character entered and even just by moving the text caret trough written notes.

[Notes]:

• The sync frequency probably causes faster battery drainage. We haven't specifically measured, but we could try.
• This also reproduces on mobile version of the experiment.
• Here is a screen recording of the issue: https://goo.gl/5V7mTR.