Ability to set the default fetch mode via the DEFAULT_FETCH_BACKEND variable

changedetectionio/model/App.py

@@ -32,7 +32,7 @@ class model(dict):
                     'password': False,
                     'base_url' : None,
                     'extract_title_as_title': False,
-                    'fetch_backend': 'html_requests',
+                    'fetch_backend': os.getenv("DEFAULT_FETCH_BACKEND", "html_requests"),
                     'global_ignore_text': [], # List of text to ignore when calculating the comparison checksum
                     'global_subtractive_selectors': [],
                     'ignore_whitespace': False,