Chore: warn users about removal of postgres v13 support (#9980)

src/paperless/checks.py

@@ -212,3 +212,31 @@ def audit_log_check(app_configs, **kwargs):
         )
 
     return result
+
+
+@register()
+def check_postgres_version(app_configs, **kwargs):
+    """
+    Django 5.2 removed PostgreSQL 13 support and thus it will be removed in
+    a future Paperless-ngx version. This check can be removed eventually.
+    See https://docs.djangoproject.com/en/5.2/releases/5.2/#dropped-support-for-postgresql-13
+    """
+    db_conn = connections["default"]
+    result = []
+    if db_conn.vendor == "postgresql":
+        try:
+            with db_conn.cursor() as cursor:
+                cursor.execute("SHOW server_version;")
+                version = cursor.fetchone()[0]
+                if version.startswith("13"):
+                    return [
+                        Warning(
+                            "PostgreSQL 13 is deprecated and will not be supported in a future Paperless-ngx release.",
+                            hint="Upgrade to PostgreSQL 14 or newer.",
+                        ),
+                    ]
+        except Exception:  # pragma: no cover
+            # Don't block checks on version query failure
+            pass
+
+    return result