fix(LeanEngine): X-LC-Prod request header

Previously, the X-LC-Prod header was `1` (production) in stage instance,
which causes data modifications in stage environment triggers
hooks in production environment.
This commit fixes this issue,
the X-LC-Prod will be set according to environment variables:

- whether in stage or production instance
- whether the user has a stage instance (when debug locally)

Related support ticket: 20333

Author: weakish

leancloud/client.py

@@ -25,7 +25,16 @@
 APP_KEY = None
 MASTER_KEY = None
 HOOK_KEY = None
-USE_PRODUCTION = '1'
+if os.getenv('LEANCLOUD_APP_ENV') == 'production':
+    USE_PRODUCTION = '1'
+elif os.getenv('LEANCLOUD_APP_ENV') == 'stage':
+    USE_PRODUCTION = '0'
+else:  # probably on local machine
+    if os.getenv('LEAN_CLI_HAVE_STAGING') == 'true':
+        USE_PRODUCTION = '0'
+    else:  # free trial instance only
+        USE_PRODUCTION = '1'
+
 USE_HTTPS = True
 # 兼容老版本，如果 USE_MASTER_KEY 为 None ，并且 MASTER_KEY 不为 None，则使用 MASTER_KEY
 # 否则依据 USE_MASTER_KEY 来决定是否使用 MASTER_KEY