🚨(backend) fix Pylint warning

Python module models.py raises too-many-ancestors warning, but linter
still pass, code is rated 10/10.

Inspired from @sampaccoud's commit #eee20032 on impress.

src/backend/.pylintrc

@@ -447,10 +447,10 @@ max-bool-expr=5
 max-branches=12
 
 # Maximum number of locals for function / method body
-max-locals=15
+max-locals=20
 
 # Maximum number of parents for a class (see R0901).
-max-parents=7
+max-parents=10
 
 # Maximum number of public methods for a class (see R0904).
 max-public-methods=20