[Feature Request] Request for REGEX validation

[amosngSP]

Is your feature request related to a problem? Please describe.
There are sometimes certain circumstances where normal options given for validation in FormSG just doesn't quite fit our use case. For example, limiting a number to 10 is not possible, as it only gives us a limit for length of the number needed.

Describe the solution you'd like
This should be clear that regex is only for advanced users. This is a good interim solution if more validation methods are being implemented into FormSG.

Describe alternatives you've considered
Hoping that the user doesn't enter a number greater than 10. Or all hell breaks loose.

Additional context
Currently, Google Forms supports this functionality to validate with custom regex.