Work around silly eventengine bug

Because:
- NAV's eventengine will not dispatch delayed alerts inside a database
  transaction, while immediate alerts are. However, the export to
  navargus occurs before the transaction is committed, which can
  result in notifications about alerts we cannot see in the database
  yet.
- The simplest workaround is to just wait a second if we cannot find
  the referenced alert.

This workaround should be removed once eventengine is fixed again.

src/navargus/__init__.py

@@ -27,6 +27,7 @@
 import re
 import logging
 import argparse
+import time
 from json import JSONDecoder, JSONDecodeError
 from typing import Generator, Tuple, List
 
@@ -170,11 +171,17 @@ def dispatch_alert_to_argus(alert: dict):
         try:
             alerthist = AlertHistory.objects.get(pk=alerthistid)
         except AlertHistory.DoesNotExist:
-            _logger.error(
-                "Ignoring invalid alerthist PK received from event engine: %r",
-                alerthistid,
-            )
-            return
+            # Workaround for eventengine bug: Its transaction is potentially not
+            # committed yet, so we wait just a little bit:
+            time.sleep(1)
+            try:
+                alerthist = AlertHistory.objects.get(pk=alerthistid)
+            except AlertHistory.DoesNotExist:
+                _logger.error(
+                    "Ignoring invalid alerthist PK received from event engine: %r",
+                    alerthistid,
+                )
+                return
 
         state = alert.get("state")
         if state in (STATE_START, STATE_STATELESS):