A key part of this is the new helper, get_user_by_delivery_email. Its
verbose name is important for clarity; it should help avoid blind
copy-pasting of get_user (which we'll also want to rename).
Unfortunately, it requires detailed understanding of the context to
figure out which one to use; each is used in about half of call sites.
Another important note is that this PR doesn't migrate get_user calls
in the tests except where not doing so would cause the tests to fail.
This probably deserves a follow-up refactor to avoid bugs here.
We add conditional infinite sleep to this delivery job as a means to
handle case of multiple servers in service to a realm running this
job. In such a scenerio race conditions might arise leading to
multiple deliveries for same message. This way we try to match the
behaviour of what other jobs do in such a case.
Note: We should eventually do something to make such jobs work
while being running on multiple servers.
Tim Abbott
Rishi Gupta
Aditya Bansal