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
Is there a reason for this change? (because if so, better to do in a separate commit + a test for the case this change was needed)