test: add clusterloader tests for atm integration

[jwtty]

What type of PR is this?
/kind test

What this PR does / why we need it:
Add scale tests for ATM integration feature. Use clusterloader2 framework.

Which issue(s) this PR fixes:

Fixes #

Requirements:

• run make reviewable for basic local test
• Read and followed fleet-networking's Code of conduct.
• uses conventional commit messages
• includes documentation
• adds unit tests

How has this code been tested

Special notes for your reviewer

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.66%. Comparing base (d633082) to head (445fcf9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #319      +/-   ##
==========================================
- Coverage   78.92%   78.66%   -0.26%     
==========================================
  Files          29       29              
  Lines        4246     4246              
==========================================
- Hits         3351     3340      -11     
- Misses        713      723      +10     
- Partials      182      183       +1     

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