Having the alert state in the message body is useful when alert topics
are not defined by alert description but encoded in the url.
E.g. in large environments having a topic for each alert [alerting] and [ok] would
make it harder to properly track if an alert has been resolved.
When each alert is in a single topic, so far, the alert state has been missing.
This change will add the current alert state and a fitting icon in front
of the alert name.(Similar to the prometheus alertmanager integration)
The test cases have been amended to cover all possible alert states, even
though realistically grafana only fires the ok and alerting states via
webhook.
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.
