Refactored sql_database (#7945)

The `sql_database.py` is unnecessarily placed in the root code folder.
A similar code is usually placed in the `utilities/`.
As a byproduct of this placement, the sql_database is [placed on the top
level of classes in the API
Reference](https://api.python.langchain.com/en/latest/api_reference.html#module-langchain.sql_database)
which is confusing and not correct.


- moved the `sql_database.py` from the root code folder to the
`utilities/`

@baskaryan

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

tests/unit_tests/test_sql_database.py

@@ -12,7 +12,7 @@ from sqlalchemy import (
     insert,
 )
 
-from langchain.sql_database import SQLDatabase, truncate_word
+from langchain.utilities.sql_database import SQLDatabase, truncate_word
 
 metadata_obj = MetaData()