Add extra fields to add-ons too. Example with Resume Manager

[iamgabrielma]

At the moment extra fields are added to the core plugin, but could also have extra fields for paid add-ons like Resume Manager. Example of email field: https://wpjobmanager.com/customization-snippets/#addEmailField

General idea:

• Check if Resume Manager is active
• If is active, enable checkbox for activate/deactivate extra field
• If enabled, pass the filter.