Add option to set payment provider settings property as mandatory

[bjarnef]

Is your feature request related to a problem? Please describe.
At the moment payment provider settings properties using PaymentProviderSetting attribute offer following properties.

• Name
• Description
• SortOrder
• View
• Key
• Config
• IsAdvanced

However it doesn't offer an option to set property as required/mandatory.

Describe the solution you'd like
It would be great to have a required/mandatory property (boolean) for PaymentProviderSetting attribute, which would mark the property with an asterisk just like when setting selecting mandatory setting on a document, media or member type?

Furthermore when a property is marked as required/mandatory and the field is empty, it could add client side validation of the form.