Feature request: Add regex validation in configurable.yml

[caalberts]

Hi,

I'd like to propose adding validation field in configurable.yml. The benefit of doing this is to avoid run time errors due to invalid configuration value. I'm thinking this can start with simple regex validation on string input, as this is where validation is most useful. Example use cases would be validating email addresses, URLs, time format, etc.

I'm happy to discuss this feature further and maybe take a stab at it.