use the new endpoint from cbc proxy. create a new task that just
serializes the event and sends it across rather than sending a template
and the broadcast message.
some changes to serialize to make it json friendly etc. it also expects
sent_at and transmitted_finishes_at to always be set (we set them in the
code but don't enforce it n the DB right now), as they're required by
utils template. not sure whether we'll update db constraints to be more
strict or utils template to be more permissive just yet, wait until we
find out more about the requirements of the CBCs we integrate with.
we won't let trial mode services send real broadcasts, and it's helpful
for users to see the flow of messages without having to have a second
person with them
new blueprint `/service/<id>/broadcast-message` with the following
endpoints:
* GET / - get all broadcast messages for a service
* GET /<id> - get a single broadcast message
* POST / - create a new broadcast message
* POST /<id> - update an existing broadcast message's data
* POST /<id>/status - move a broadcast message to a new status
I've kept the regular data update (eg personalisation, start and end
times) separate from the status update, just to keep separation of
concerns a bit more rigid, especially around who can update.
I've included schemas for the three POSTs, they're pretty
straightforward.
