Update ExternalBeamPlanning module to use markup ROI instead of annotation ROI

[lassoan]

Annotations module, which provides vtkMRMLAnnotationROI and vtkMRMLAnnotationRuler nodes have been deprecated since April 2021 and will be removed in Slicer-5.4 stable version early next year.

ExternalBeamPlanning module uses annotation ROI node in ExternalBeamPlanning\Resources\UI\qSlicerExternalBeamPlanningModule.ui. This module need to be updated to use markups nodes before the end of this year.

This section of the migration guide should help with implementing the changes and any questions can be asked at the Remove Annotations module topic in the Slicer forum.