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.

Screenshots

Assignee dropdown

Before	After

Reviewer dropdown

Testing Locally

1. Have AI features working
2. Setup the agent to showup as an assignee account. You can do it the normal way, or hacky way
   1. Normal, but harder
      1. Setup a service account/agent
      2. Setup a trigger on assignee or reviewer
3. In a merge request, open the assignee dropdown
4. Notice the agent has the label
5. open the reviewer dropdown
6. Notice the agent has the label