Support mock APNS in osquery-perf

[MagnusHJensen]

Related issue: Resolves #31313

Checklist for submitter

If some of the following don't apply, delete the relevant line.

• Changes file added for user-visible changes in changes/, orbit/changes/ or ee/fleetd-chrome/changes.
  See Changes files for more information. Internal only change

• Input data is properly validated, SELECT * is avoided, SQL injection is prevented (using placeholders for values in statements), JS inline code is prevented especially for url redirects, and untrusted data interpolated into shell scripts/commands is validated against shell metacharacters.

• Timeouts are implemented and retries are limited to avoid infinite loops

• If paths of existing endpoints are modified without backwards compatibility, checked the frontend/CLI for any necessary changes

Testing

• Added/updated automated tests
• QA'd all new/changed functionality manually

[codecov]

Codecov Report

❌ Patch coverage is 8.18182% with 101 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.64%. Comparing base (7bf008f) to head (3562f7c).

Files with missing lines	Patch %	Lines
cmd/osquery-perf/agent.go	0.00%	98 Missing ⚠️
pkg/mdm/mdmtest/apple.go	75.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           31311-fleet-mock-apns   #51130      +/-   ##
=========================================================
- Coverage                  68.65%   68.64%   -0.01%     
=========================================================
  Files                       4000     4000              
  Lines                     258102   258132      +30     
  Branches                   13839    13839              
=========================================================
+ Hits                      177197   177205       +8     
- Misses                     65153    65175      +22     
  Partials                   15752    15752              

Flag	Coverage Δ
backend	69.74% <8.18%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 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.