Dashboards can now have a description. We need to add this field to the Dashboards definition. This field can be empty, and can have a maximum 400 characters.

ATs:

• Dashboards can have a description saved
• Existing Dashboards are migrated to have a null value for that field
• Dashboards cannot have descriptions with greater number of characters than 400
• Dashboards Descriptions can be updated by those with authorization
• REST-API docs are updated

Testing Notes:

• Dashboards can have a description
• Dashboards cannot have a description containing more than 400 characters
• Dashboard descriptions can be updated
• Existing dashboards do not have a description by default
• Dashboards can be imported with a description