Show composite accounts as agents in MRs

Description

This code change adds support for displaying "Agent" badges next to user names throughout the GitLab interface. When a user has a special "composite identity enforced" property (meaning they're acting as an automated agent rather than a regular human user), a small gray "Agent" badge will now appear next to their name in various places like assignee dropdowns, user lists, and autocomplete suggestions. The change updates both the frontend display components and the backend data queries to include this new agent identification feature, helping users distinguish between human users and automated agents in the system.

How to reproduce

Screenshots

Assignee dropdown

Before	After

Reviewer dropdown