[Bug] Update Rule Formatter (#3668)

* Update Rule Formatter

* Only apply fix to Note

(cherry picked from commit 094ef22604)

detection_rules/rule_formatter.py

@@ -216,6 +216,11 @@ def toml_write(rule_contents, outfile=None):
                 preserved_fields = ["params.message"]
                 v = [preserve_formatting_for_fields(action, preserved_fields) for action in v]
 
+            if k == 'note' and isinstance(v, str):
+                # Transform instances of \ to \\ as calling write will convert \\ to \.
+                # This will ensure that the output file has the correct number of backslashes.
+                v = v.replace("\\", "\\\\")
+
             if isinstance(v, dict):
                 bottom[k] = OrderedDict(sorted(v.items()))
             elif isinstance(v, list):