Update existing custom field values if setting a new default value

Problem Definition

When creating a new configuration context and setting a default value for a custom field, this does not affect any custom fields in issues that were created before the default was set.

Instead it will only set the default value for any newly created issues

Suggested Solution

If a new context and default value is set, and an existing ticket does not have a value for the field. The field should get the new default value.