[MU] Save draft locally periodically

[chibenwa]

Description

On WEB:

GIVEN I type a message
AND stop typing for 15 seconds
THEN twake mail saves the email locally (not on the JMAP server)

That way if the broswer crash (eg power failure) then the email is not lost.

When reopening the browser the composer should be reopened with user input.

Ref: https://github.com/Yash18-hub/CISD-GES/issues/88

Let's not save on the back as it might create a massive surge in requests