Annotations : Make iframe wrapper configurable [CORE]

SUMMARY

Annotations sidebar is always attached to the body of the DOM, this creates issues for the AngularUI components, and for this reason it needs to be made configurable so that the DOM element to which the frame will be attached can be defined by configuration.

Note: this issue is about the Angular implementation, which depends on the changes made in https://code.europa.eu/leos/annotate/-/merge_requests/117.