ENH: dtype costumization on to_sql (GH8778)

This is the proposed general gist of the changes. My ad-hoc testing suggests that this might work. If this is an acceptible design, I will proceed to make the formal test and change the docs (including docstrings)

Closes #8778
Can you put this in `_TestSQLAlchemy` (then it will be also run for the other database flavors)