Support multi-select refdata properties in Agreement settings

Purpose:
To enable an ERM admin to add supplementary properties with multi-select refdata type

User story statement(s):

As a ERM admin
I want to add a supplementary property with the multi-select pick list type
so that users can use the property in an agreement

Wireframe

Scenarios:

1. Scenario:
   • Given Settings -> Agreements -> Supplementary Properties
   • When I click "Create" to create a new property
   • Then I see the property creation form
2. Scenario:
   • Given the property creation form
   • When I view the list of options in the "Type" menu
   • Then I see the option to select an option "Pick list (multi-select)"
3. Scenario:
   • Given the property creation form
   • When I select the type "Pick list (multi-select)"
   • Then I see an option to select a Picklist (as per the current behaviour of the Refdata type)
4. Scenario:
   • Given the property creation form with the type "Pick list (multi-select)" specified
   • When I have completed all required fields for the form
   • Then I can create the new property by clicking "Save"

All other behaviour of the form is in line with the current behaviour (i.e. no change to required fields and validation etc.)