🔧(backend) allow to configure psycopg pool timeout

We want to allow the configuration of the psycopg pool timeout.
For this we created a new setting DB_PSYCOPG_POOL_TIMEOUT

src/backend/impress/settings.py

@@ -110,6 +110,11 @@ class Base(Configuration):
                         environ_name="DB_PSYCOPG_POOL_MAX_SIZE",
                         environ_prefix=None,
                     ),
+                    "timeout": values.IntegerValue(
+                        3,
+                        environ_name="DB_PSYCOPG_POOL_TIMEOUT",
+                        environ_prefix=None,
+                    ),
                 }
             },
         }