You'd use a validator for that. Example is here: https://academy.creatio.com/docs/8.x/dev/development-on-creatio-platform/platform-customization/freedom-ui/customize-page-fields/examples/implement-the-field-value-validation

There's plenty of examples of javascript regex to validate a URL online that you could use, depending on how you want to enforce a URL (such as must start with protocol http otr https or just allow www.domain.com, or even domain.com). 

Sadly, there's no way to implement it globally for any/all link fields.

Ryan