ServiceX DID finder

[ponyisi]

Returns URLs from ServiceX output store so they can be used as input to further transforms. Closes #342 (though this does not stream as a transform completes, it is strictly one-shot).

[codecov]

Codecov Report

❌ Patch coverage is 97.80220% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.65%. Comparing base (c3c5b5e) to head (a28a02f).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ervicex/src/servicex_did_finder_servicex/celery.py	95.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1552      +/-   ##
===========================================
+ Coverage    89.48%   89.65%   +0.17%     
===========================================
  Files          106      108       +2     
  Lines         3833     3916      +83     
  Branches       470      470              
===========================================
+ Hits          3430     3511      +81     
- Misses         326      328       +2     
  Partials        77       77              

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