feature: A parameter for isDateString

[yanmarinich]

Description

The problem is ORM level like prisma which has DateTime type so string like 2023-09-25 is valid for class-validator but invalid for Prisma which leads to exception "Invalid value for argument startsAt: premature end of input. Expected ISO-8601 DateTime."

Proposed solution

Add an extra parameter something like isDateTime which checks if a string has time.

[recallwei]

Face the same problem.