Reporting - filter by collections

[#1]

NEED: Project Report FILTERED to show only Projects that contain a specific Milestone from a specific Milestone Path. This needs to be a project report because we are reporting on several collections at once.

PROBLEM: Since the milestone lives on the Task object and not the Project object, this filter is impossible.

SOLUTION: filter by collections; the ability to look within a collection of a project (Tasks, Milestones, etc...) and include or exclude results from a Project report based on these criteria.

Potentially similar idea: https://one.workfront.com/s/idea/0870z000000PSu3AAG/detail