🔧(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

Author: lunika

docs/env.md

@@ -48,6 +48,7 @@ These are the environment variables you can set for the `impress-backend` contai
 | DB_PORT                                         | Port of the database                                                                                                                                                       | 5432                                                                    |
 | DB_PSYCOPG_POOL_MIN_SIZE                        | The psycopg min pool size                                                                                                                                                  | 4                                                                       |
 | DB_PSYCOPG_POOL_MAX_SIZE                        | The psycopg max pool size                                                                                                                                                  | None                                                                    |
+| DB_PSYCOPG_POOL_TIMEOUT                         | The default maximum time in seconds that a client can wait to receive a connection from the pool                                                                           | 3                                                                    |
 | DB_USER                                         | User to authenticate with                                                                                                                                                  | dinum                                                                   |
 | DJANGO_ALLOWED_HOSTS                            | Allowed hosts                                                                                                                                                              | []                                                                      |
 | DJANGO_CELERY_BROKER_TRANSPORT_OPTIONS          | Celery broker transport options                                                                                                                                            | {}                                                                      |

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,
+                    ),
                 }
             },
         }