APIAP: Option to create that API acts as product

We need to add a checkbox "Act as product" field in the "New API" form.

• The value will set the field act_as_product of the service
• It should be available only when creating a new API (not on edit)
• It should be available only for providers with api_as_product RU enabled
• If this checkbox is selected, we need to display a Select with:

• New Backend API (this one will crate a new backend api for this service)
  [ list with all backend apis for this account]