Update the New Relic webhook and tests to match the format specified
in the New Relic documentation. The new format sends a json body
instead of using url parameters. The old format is no longer supported
by New Relic according to their support staff; as a result, the fixtures for
the old test cases were removed. Added fixtures for new test cases.
Fixes: #16393.
Almost all webhook tests use this helper, except a few
webhooks that write to private streams.
Being concise is important here, and the name
`self.send_and_test_stream_message` always confused
me, since it sounds you're sending a stream message,
and it leaves out the webhook piece.
We should consider renaming `send_and_test_private_message`
to something like `check_webhook_private`, but I couldn't
decide on a great name, and it's very rarely used. So
for now I just made sure the docstrings of the two
sibling functions reference each other.
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>