Add offboard cmd for coder as well

[amrit110]

This pull request adds a new offboard-users subcommand to the onboard admin CLI tool, enabling administrators to offboard Coder users who are no longer members of a specified GitHub organization. The implementation includes comprehensive CLI argument parsing, integration with the offboarding logic, and a full suite of tests to ensure correct behavior and argument handling.

New CLI functionality:

• Added the offboard-users subcommand to src/aieng_platform_onboard/admin/cli.py, with arguments to control organization, dry-run mode, account suspension, workspace and Firestore cleanup, and error handling options.
• Integrated the new subcommand with the offboard_users_from_org function, passing through all relevant arguments.
• Imported the offboard_users_from_org function for use in the CLI.

Testing:

• Added a comprehensive test class TestOffboardUsersCommand in tests/aieng_platform_onboard/admin/test_cli.py, covering all CLI argument combinations, error cases, and help output for the new offboard-users command.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.85%. Comparing base (79bf027) to head (ad9213e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #83      +/-   ##
==========================================
+ Coverage   90.62%   91.85%   +1.22%     
==========================================
  Files          10       11       +1     
  Lines        1408     1620     +212     
==========================================
+ Hits         1276     1488     +212     
  Misses        132      132              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.