CDM-458: Add mongo methods for cleaning up refdata transient files

[MrCreosote]

Needed to alter refdata saving / adding a refdata site so that the cleaned field is persisted per cluster and the nersc task ID field is not initialized as null, which prevents $push operations

[codecov]

Codecov Report

❌ Patch coverage is 84.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.62%. Comparing base (19f25ff) to head (e10a573).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cdmtaskservice/refdata.py	0.00%	3 Missing ⚠️
cdmtaskservice/jobflows/nersc_jaws.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #526      +/-   ##
==========================================
+ Coverage   53.48%   53.62%   +0.14%     
==========================================
  Files          69       69              
  Lines        5845     5863      +18     
==========================================
+ Hits         3126     3144      +18     
  Misses       2719     2719              

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