[Feature Request]: Re-Implement Mail Validator Transform

### What would you like to happen?

In Kettle there was a Mail Validator transform ("step") for use in pipelines (not to mix up with the feature with the same name for use in workflows). This allowed for some checking of valid e-mail addresses. Since e-mail address validation seems to be something sophisticated in terms of regex, and as for the not-aware (who is?) the solution situation is somehow intransparent, it might be a good idea to re-implement this feature in a future version.

### Issue Priority

Priority: 3

### Issue Component

Component: Hop Gui

No file or test is named. Start by locating the existing Mail Validator workflow feature and the corresponding Kettle step in Hop Gui, then compare their pipeline integration. Establish the supported email-validation behavior and tests before implementation; done means a pipeline transform is available with documented, passing coverage.

Written by the indexing model from the issue text.