Add CONN_MAX_AGE to documentation (#3642)

* Add CONN_MAX_AGE to sample configurations

* Correct alignment

* Restore ghost space

* Correct alignment.

* Use stable docs url

netbox/netbox/configuration.example.py

@@ -17,6 +17,7 @@ DATABASE = {
     'PASSWORD': '',           # PostgreSQL password
     'HOST': 'localhost',      # Database server
     'PORT': '',               # Database port (leave blank for default)
+    'CONN_MAX_AGE': 300,      # Max database connection age
 }
 
 # This key is used for secure generation of random numbers and strings. It must never be exposed outside of this file.