Gateway disconnect notification timeout not respected

[voyvodov]

Describe the bug
The env variable DEFGUARD_GATEWAY_DISCONNECTION_NOTIFICATION_TIMEOUT is not respected by the core.
No matter what value is put, notification is always send even for a simple gateway restart.

To Reproduce
Steps to reproduce the behavior:

1. Add gateway
2. Put DEFGUARD_GATEWAY_DISCONNECTION_NOTIFICATION_TIMEOUT=1h for an example in /etc/defguard.core.conf file.
3. Configure SMTP
4. Restart the gateway (which takes <1 minute).
5. You'll get an email immediately.

Expected behavior
Defguard should sent notification only if the gateway is disconnected for the specific time.

Version information

• Defguard Core version: v1.1.0
• Defguard Gateway version: v1.1.0
• Operating system and version running the gateway: Ubuntu 20.04