Acknowledge alarms (mute and track)

Acknowlege alarms and mute notifications for a defined duration, so that no notifications are sent for alarms that are actively investigated by a responsible person or tracked by a ticket.

Concept

The _acknowledgement_ of an alarm means that an external entity has taken over responsibility for solving the underlying issue, so that it no longer necessary to send notifications on the alarm state. This acknowledgement holds as long as the alarm state does not change and the MPT is not exceeded.

Proposed Design

The fact that an alarm has been acknowledged shall be modelled as a new alarm state. This state controls the behaviour of the thresholder and the notification engine. Alarms in state ACK are left untouched until they are either deleted or their MPT expires (this implies that an alarm gets a new attribute) The notification engine will send notifications for the ACK state-change (if requested) as well as for the final resolution of the alarm, but not periodic ones.

Requirements

- [ ] Acknowledged alarms gain a special alarm stated ACKNOWLEDGED
    - [ ] Notifications about the acknowledgement can be requested the same way as for other states
- [ ] The user acknowledging the alarm is assigned to the alarm as responsible
    - [ ] Responsible user is displayed in alarm inspector (Alarm / Show)
- [ ] Acknowledged alarms can be assigned to a ticket (via ticket URL)
- [ ] Notifications for acknowledged alarms can be muted for a limited time
    - [ ] Alarms that are muted do not send periodic notifications
    - [ ] Alarms that are muted do not send notifications even when the result of the alarm expression changes
    - [ ] Acknowledgement of alarms is logged with user ID, mute-duration and optionally ticket-link (severity INFO)