Feat: add response error when tribe already exists

backend/repository/tribe_sqlite_repository.py

@@ -2,11 +2,21 @@ from backend.model.tribe import Tribe
 from backend.repository.abstract_repository import AbstractRepository
 
 
+class TribeRepositoryError(Exception):
+    pass
+
+
 class TribeSQLiteRepository(AbstractRepository):
     def __init__(self, conn) -> None:
         self.conn = conn
 
     def add(self, tribe: Tribe) -> None:
+        tribes = self.list()
+        if tribe.name in map(lambda x: x.name, tribes):
+            raise TribeRepositoryError(
+                f"The tribe {tribe.name} already exists. Can't add it"
+            )
+
         self.conn.execute(
             """
         INSERT INTO tribes(name, level) VALUES (?, ?)