Epic data model

Epics will evolve over time. Many of the proposed features are here: https://gitlab.com/gitlab-org/gitlab-ee/issues/3254.

A listing of features we expect epics to have, that will make them similar to issues:

• Promote issue to an epic.
• Demote epic to an issue.
• Project-level epics.
• Title and description fields.
• Start date and end date.
• System notes.
• Comment thread.
• Sidebar.
• Todo.
• Labels.
• Weight which is combined weight of issues.
• Confidentiality.
• Subscriptions and notifications.
• Integration with milestones.
• Assigning to a team or individual.
• Epics contained in epics, i.e.:

We’d want to do infinite subbing/nesting downard, where “infinite” means we would set some arbitrary limit (like 20 for subgroups right?). THis is the typical for port mgmt tools to give that felxibility of any type of work breakdown structure you want. tldr: epics would be internal nodes in a tree structure, issues would be the leaves