Create ability to create and Link a Portfolio Epic directly from Theme like Objectives

Today it is already possible to create or link an objective from the Theme, but to link a Portfolio Epic you have to go into the Portfolio Epic to do that.

Later in the work tree you see Themes linking to Work Items, so we do support the linking between the two item types but just have one option to create them which causes difficulties for the customers. Especially since OKRs which also link to Themes have that option to be created or linked on theme level