message: chore(docs):  remove .py from db migrate -m
  no need to state the python extension
  before: add_metadata_column_to_annotation_model.py.py
  after: add_metadata_column_to_annotation_model.py
diff: @@ -1137,7 +1137,7 @@ Submissions will be considered for submission (or removal) on a case-by-case bas
  1. Generate the migration file
  ```bash
  - superset db migrate -m 'add_metadata_column_to_annotation_model.py'
  + superset db migrate -m 'add_metadata_column_to_annotation_model'
  ```
  This will generate a file in `migrations/version/{SHA}_this_will_be_in_the_migration_filename.py`.
  