Broadcast every change through HTTP

[alenkacz]

We have Seyren integrated with Icinga - where we have our alerts and escalations. Icinga and Seyren are connected through HTTP subscription.

In order to do proper escalations, we need the HTTP subscription to be triggered on every Seyren check, not just when state changes.

I analyzed it and the easiest solutions seems adding new subscription type - Http Broadcast, that will broadcast the state all the time - which even opens the possibility of other integrations.

I'll prepare PR.