SQLAlchemy bad error handling

SQLAlchemy doesn't give us the right "confort" for error handling. We need to handle it depending on which db engine we are using, and we need to use test like `"text in the error detail" in e.details`. For later, we'll need to find a better way.

# Context from PR

If we check if an error is an instance of another module `pymysql` we *could potentially* catch some errors as code that are specific on a `db`. And even with that, I saw errors where people had to use both `IntegrityError` from sql-alchemy and `pymy` integrity error because of a bad handling..

It is not pretty, and you can read this response: https://stackoverflow.com/a/70714697

_Originally posted by @Robin-Van-de-Merghel in https://github.com/DIRACGrid/diracx/pull/421#discussion_r2028828354_