Dashboard: implement widget sharing

Current situation or problem:

In the initial dashboard implementation all users have their own dashboards and widgets. There is no way to share the work of configuring a widget and having that made available for multiple users. This feature is to implement mechanisms for:

• Widget instance sharing (where widget instances from other users can be found and copied)

In scope

• Sharing widget instances including
  • Method to make a widget instance configuration available for others to copy
  • Method to find available widget instance configurations to copy
  • Ability to copy an existing widget instance configuration to a dashboard

Out of scope

Any other widget/dashboard copying or sharing