fix: strip whitespace and handle null values in instance configuration

When patching instance configuration values, the raw values from
request.data were used directly without sanitization. This adds:
- Whitespace stripping via str().strip() to prevent leading/trailing
  spaces from being stored
- Explicit None handling so that null values become empty strings
  instead of the literal string "None"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: okxint

apps/api/plane/license/api/views/configuration.py

@@ -45,7 +45,8 @@ def patch(self, request):
 
         bulk_configurations = []
         for configuration in configurations:
-            value = request.data.get(configuration.key, configuration.value)
+            raw_value = request.data.get(configuration.key, configuration.value)
+            value = "" if raw_value is None else str(raw_value).strip()
             if configuration.is_encrypted:
                 configuration.value = encrypt_data(value)
             else: