Trello Integration: Static string mapping

Hi,

Trello Integration is already cool, we can flexibly map various Trello fields to various Aha fields, and for some fields also specify how particular Trello values map to particular Aha values.

However, this still assumes that for every Aha field there is a corresponding Trello field and vice versa. That is not always the case and sometimes it would be helpful to specify a default static value that will be insterted in Aha. For example, Release = "Summer 2019". 

Otherwise, we have to go repeatedly to all new records created by the integration and manually populate the fields that are not mappable to Trello because that type of info is simply not managed there.