May be related to #7849

Sometimes a more complex issues relation is needed as it is available in Redmine. Real life example: we are moving to a new office, so we have a list of renovation related issues, among them 1) Build-up (like internal walls painting) and 2) Air condition split system. The start date of this two issues are not directly related, we can start them independently in parallel. However, the set up of the internal air conditioning unit can only be done after the build-up is finished (the external unit and the link can be installed beforehand). So the relation type needed is "Due date follows": Air condition issue due date follows the build-up issue (its due date as usual) by XX days.

As a workaround, I can split the second issue into two "Condition without the setup of the internal unit" and "Setup the internal unit of condition", however, this adds an excessive level of details to the plan (as soon as the conditioning is done by the 3rd party, I do only need the date they will start the setup and finish it).