Use explicit format string, that contains milliseconds, when
converting an QDateTime/QTime to a SQLite field content.

Task-number: QTBUG-24200
[ChangeLog][QtSql][QSQLITE] Fix sub-second handling
Change-Id: Ib89152b7c3dd780b57a8826beff8b6b118e9d3d6
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Mark Brand <mabrand@mabrand.nl>