Collections

**User story**
As a user or leader I want to save and share collections of processes or filter of processes so that I and my team can find our relevant processes. Each collection page has metrics to it.

**Describe the solution you'd like**
Add a collection on the sidebar below all, my and favourites. Name, icon, sharing? Example: Lean DPO, mad team etc.
- Manual collections: Drag and drop processes to a collection.
- Smart collections: Filtered collections like in Smart folders in the Photos app on a mac.

The issue does not name files, tests, or entry points. First clarify the collection model and scope for manual collections, smart filtered collections, sidebar placement, sharing, and per-collection metrics. Done would require an agreed design and implementation covering those behaviors, but the issue is too broad and has had no recent activity for a first contribution.

Written by the indexing model from the issue text.