Add feature suggesting parent task for Redmine

[jun66j5]

When entering "parent task", Redmine suggests issues by filtering the entered text. However, fulmo extension couldn't suggest and should do it.

[hendrik-schumacher]

This would be quite useful since one needs to look up the parent issue ids manually atm. It would also be cool if you could specify a default parent issue id in the settings. We use a backlog plugin for redmine that needs us to set parent issue ids for all newly created tickets.