Migrations: Implement adapter method delete_field_from_each_document

[eecavanna]

Adapter method signature:

def delete_field_from_each_document(
    self,
    collection_name: str,
    field_name: str,
) -> None:
    r"""
    Deletes the specified field from each document in the collection.
    """
    pass

Mongo query (docs):

db.collection.updateMany({}, {$unset: {foo: 1}}); // delete `foo` field from each document