Moved cleanup to api (#50142)

Author: aritra24

airflow-core/src/airflow/api_fastapi/core_api/datamodels/dags.py

@@ -17,6 +17,7 @@
 
 from __future__ import annotations
 
+import inspect
 from collections import abc
 from collections.abc import Iterable
 from datetime import datetime, timedelta
@@ -164,6 +165,14 @@ def get_timezone(cls, tz: Timezone | FixedTimezone) -> str | None:
             return None
         return str(tz)
 
+    @field_validator("doc_md", mode="before")
+    @classmethod
+    def get_doc_md(cls, doc_md: str | None) -> str | None:
+        """Clean indentation in doc md."""
+        if doc_md is None:
+            return None
+        return inspect.cleandoc(doc_md)
+
     @field_validator("params", mode="before")
     @classmethod
     def get_params(cls, params: abc.MutableMapping | None) -> dict | None: