DM-53292: Add wmsAttemptNum via generic wms variables.

[MichelleGower]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.93%. Comparing base (205b7eb) to head (ff74d82).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #222      +/-   ##
==========================================
+ Coverage   89.82%   89.93%   +0.11%     
==========================================
  Files          51       51              
  Lines        5464     5496      +32     
  Branches      539      540       +1     
==========================================
+ Hits         4908     4943      +35     
+ Misses        457      455       -2     
+ Partials       99       98       -1     

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