Add field iteration into Issue

[KoCoder]

In Issue #912 you've implemented the iteration into the Issuefilter.
Problem: I'd like to access set Iterations. Currently only filtering by Iterations is possible.
Maybe adding a String field with the Iteration Title to the Issue Class.

Later today, I'll implement that and create an MR, anything I should look out for?

[jmini]

This will be a good addition. Thank you.