Generated by `pyupgrade --py3-plus --keep-percent-format` on all our
Python code except `zthumbor` and `zulip-ec2-configure-interfaces`,
followed by manual indentation fixes.
Signed-off-by: Anders Kaseorg <anders@zulipchat.com>
This is preparatory work for settings controlling who can see user
emails; it includes the API-level support for editing it, but no code
to actually enforce the policy.