[FE] Define a segment in DevOps Report

Problem

One of the most important aspects of the feature proposed in &4169 (closed) is the ability to create custom segments. These could be a subset of members working on a monorepo, or a series of multiple projects that are managed and built by a particular team.

Proposal

Empty state	Modal	Table	Tooltips & dropdown menu	Toast

Create a "Segments" button on the DevOps Report page. This should expose a modal that allows me to create a new segment. Confirm submission with toast message "Segment created".

This is the frontend portion. backend issue is #262395 (closed)

Scope of this iteration:

1. Page in admin section (will later be moved to instance-level)
   • Newly created segments should appear on the DevOps Report page.
2. Empty state
3. Modal to define segments (top-level groups only in first iteration)
   • Constraint handling: Constrain segments to contain 20 max groups only (top-level)
4. Add segment button
   • Disable and add tooltip when table rows = 30.
5. Add segment row to table
   • Number of segments in table (max): 30
6. Confirmation toast when new segment is created

Later iterations:

• Edit segment
• Delete segment

Questions

If we update the data overnight, what should we do with an immediately created segment?