Re-send notifications previously suppressed by their time periods

[Al2Klimov]

fixes #6167
fixes #7099

[N-o-X]

Works as expected. Please add documentation about event::SetSuppressedNotificationTypes to the JSON-RPC Message API section in Technical Concepts.

[dnsmichi]

When the docs are updated and @lippserd agrees, we can move this to 2.12.

[Al2Klimov]

Will add docs, but I don't agree with adding this to v2.12.

[N-o-X]

Forgot my test protocol.

Config:

object Host "notification-test-host" {
  check_command = "dummy"
  enable_active_checks = false
  max_check_attempts = 1
}

object TimePeriod "exthours" {
  ranges = {
    "friday" = "11:15-17:00"
  }
}

object User "test-user" {
}

apply Notification "host-exthours" to Host {
  interval = 1d
  command = "mail-host-notification"

  period = "exthours"
  users = [ "test-user" ]

  assign where host.name == "notification-test-host"
}

Test:

Processing check result with exit status 1:

curl -k -s -u root:icinga -H 'Accept: application/json' \
 -X POST 'https://localhost:5665/v1/actions/process-check-result' \
 -d '{ "filter": "host.name==\"notification-test-host\"", "type": "Host", "exit_status": 1, "plugin_output": "Host is not available." }'

Results in:

[2020-02-14 11:13:10 +0100] notice/Notification: Attempting to send notifications of type 'Problem' for notification object 'notification-test-host!host-exthours'
[2020-02-14 11:13:10 +0100] notice/Notification: Not sending notifications for notification object 'notification-test-host!host-exthours': not in timeperiod 'exthours'

2 Minutes later (in TP):

[2020-02-14 11:15:00 +0100] notice/NotificationComponent: Attempting to re-send previously suppressed notification 'notification-test-host!host-exthours'.
[2020-02-14 11:15:00 +0100] notice/Notification: Attempting to send notifications of type 'Problem' for notification object 'notification-test-host!host-exthours'.

[Al2Klimov]

Feel free to merge.