[FR] Loosen Filters Schema Validation (#3753)

(cherry picked from commit 259efaf716)

detection_rules/rule.py

@@ -310,6 +310,9 @@ class Query:
 
 @dataclass(frozen=True)
 class Filter:
+    """Kibana Filter for Base Rule Data."""
+    # TODO: Currently unused in BaseRuleData. Revisit to extend or remove.
+    # https://github.com/elastic/detection-rules/issues/3773
     meta: FilterMeta
     state: Optional[FilterStateStore] = field(metadata=dict(data_key="$state"))
     query: Optional[Union[Query, Dict[str, Any]]] = None
@@ -343,7 +346,7 @@ class BaseRuleData(MarshmallowDataclassMixin, StackCompatMixin):
     exceptions_list: Optional[list]
     license: Optional[str]
     false_positives: Optional[List[str]]
-    filters: Optional[List[Filter]]
+    filters: Optional[List[dict]]
     # trailing `_` required since `from` is a reserved word in python
     from_: Optional[str] = field(metadata=dict(data_key="from"))
     interval: Optional[definitions.Interval]