Ability to Bucket Work Item into groups and Filter

**Is your feature request related to a problem? Please describe.**
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

**Describe the solution you'd like**
Ability to Create a Buckets like Epics or Sprints. Each bucket(Epic or Sprint) has work items under it. We can do this now outside devops center. But within Devops center there is no way to filter these using custom fields inside Pipeline page.

**Additional context**
We can create the frame work outside Devops center as work items are custom objects. But, within DevOps center, we need the ability to group/filter work items on pipelines page and workitems page.