[schema] Use TZDatetime for creation_date and modification_date
No work has been done for form fields/widgets since creation_date /
modification_date are by default not editable through the default UI. One may
want to add such feature at some point.
Time will be displayed as UTC, let the end-application decide otherwise by
customizing the tzdatetime printer if desired.
Closes #4848923
option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')