fix ascii codec error, by using utf8 (#1608)

Co-authored-by: crazywoola <427733928@qq.com>

api/config.py

     'DB_HOST': 'localhost',
     'DB_PORT': '5432',
     'DB_DATABASE': 'dify',
+    'DB_CHARSET': 'utf8mb4',
     'REDIS_HOST': 'localhost',
     'REDIS_PORT': '6379',
     'REDIS_DB': '0',
         # ------------------------
         db_credentials = {
             key: get_env(key) for key in
-            ['DB_USERNAME', 'DB_PASSWORD', 'DB_HOST', 'DB_PORT', 'DB_DATABASE']
+            ['DB_USERNAME', 'DB_PASSWORD', 'DB_HOST', 'DB_PORT', 'DB_DATABASE', 'DB_CHARSET'']
         }
 
-        self.SQLALCHEMY_DATABASE_URI = f"postgresql://{db_credentials['DB_USERNAME']}:{db_credentials['DB_PASSWORD']}@{db_credentials['DB_HOST']}:{db_credentials['DB_PORT']}/{db_credentials['DB_DATABASE']}"
+        self.SQLALCHEMY_DATABASE_URI = f"postgresql://{db_credentials['DB_USERNAME']}:{db_credentials['DB_PASSWORD']}@{db_credentials['DB_HOST']}:{db_credentials['DB_PORT']}/{db_credentials['DB_DATABASE']}?client_encoding={db_credentials['DB_CHARSET']}"
         self.SQLALCHEMY_ENGINE_OPTIONS = {
             'pool_size': int(get_env('SQLALCHEMY_POOL_SIZE')),
             'pool_recycle': int(get_env('SQLALCHEMY_POOL_RECYCLE'))