Edit existing dashboard widget instance

Description:

• Amend an existing widget instance configuration 

Development Tasks:

1. Action link / button to enter edit UI
2. Edit page using existing forms but with non-relevant fields disabled
3. Submit of edit form PUT functionality working as expected

Constraints / Checks:

• Can be edited by dashboard owner (not widget creator), or a system administrator
  • Users can only see their own dashboard, so it should not be possible to edit other users' widget instances
• Definition cannot be edited 
• Edited widget must meet minimum validation (as per Create), as defined by widgetType
  • For SimpleSearch: at least 1 column returned
• There is no widgetInstance configuration history - changes overwrite existing configuration
  • Cloning or duplicating widgets is out of scope at this stage
• Widget manipulation is tied to individual users permissions