Dashboard: Prevent columns being added more than once in a simple search widget

Purpose
Prevent duplicate columns being added to a simple search widget.

Description
When creating a new/editing a widget of the Type "Simple Search" multiple columns can be added for display in the widget. Currently it is possible to add each column more than once, creating duplicates in the table. Instead this should be prevented.

When a duplicate column is added by the user, the validation error message "Duplicate column, please rectify" should be displayed for each of the duplicates, as shown in the mockup.

The message should be displayed when the duplicate column is present and the form fails validation when closing. selected, i.e. real time validation.

When a duplicate column is reordered, the error message should move with the column.

Any duplicates must be removed before the widget can be saved.

This change affects the widget definitions ERM Licenses and ERM Agreements.

Dev task breakdown

• Do we definitely want a validation error instead of just not displaying any columns currently in the list? YES > VALIDATION 
  • If we actually want the latter, we recently did something similar in stripes-erm-components
  • If we want the former then we can just add a validation to the fieldArray here