Modernize approval process: Remove CODEOWNERS to enable team-wide contributions

Summary

This MR removes the CODEOWNERS file to simplify the approval process and enable broader team participation.

Motivation

Due to advances in the Duo Agentic Platform, we should let anyone on the team contribute. The previous CODEOWNERS requirement for specific individuals (@adam-gitlab and @katrinleinweber-gtlb) created unnecessary bottlenecks.

With AI-assisted code review and improved tooling, any team member can effectively review and approve changes.

Changes

• Removes CODEOWNERS file
• Allows any maintainer to approve merge requests
• Reduces approval friction while maintaining code quality through standard review processes

Related Issues

• #45 (closed)
• #41