Set two or more “Email/URL candidature” for each new job in WP Job Manager

### Is your feature request related to a problem? Please describe
The application email field is only designed to hold one email address.
Using a , (comma) on the frontend submission doesn't work. However, when I add two email addresses (ex: [name@domain.com](mailto:name@domain.com), [anothername@domain.com](mailto:anothername@domain.com)) on the backend, WP Job Manager tries to parse one of it as a URL. I'm not able to add two email addresses to the field.

### Describe the solution you'd like
I need to add two email addresses to the field.

### Describe alternatives you've considered
I've no alternative solutions...

### Additional context
Add any other context or screenshots about the feature request here.

Start with the application email field handling for frontend submission and backend editing, then reproduce the comma-separated and two-address cases described in the issue. Done means two or more email addresses can be entered and retained without one being parsed as a URL.

Written by the indexing model from the issue text.