Support custom ado fields that mark work items as duplicate

[kananb]

Summary of the Pull Request

Adds a new field to the ado config to specify work item fields that indicate a work item is marked as a duplicate.

PR Checklist

• [x] Applies to work item: #3384
• [ ] CLA signed. If not, go over here and sign the CLI.
• [ ] Tests added/passed
• [x] Requires documentation to be updated
• [ ] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Info on Pull Request

What does this include?

Validation Steps Performed

Set a bug to "Completed" with the reason "Testing", and verified that it was reopened when a bug with the same title was filed again with an ado config that included "Sytem.Reason": "Testing" in the "ado_duplicate_fields" property.

[codecov-commenter]

Codecov Report

Merging #3467 (b3d604a) into main (7b40402) will decrease coverage by 0.01%. The diff coverage is 27.27%.

@@            Coverage Diff             @@
##             main    #3467      +/-   ##
==========================================
- Coverage   34.42%   34.42%   -0.01%     
==========================================
  Files         299      299              
  Lines       36253    36259       +6     
==========================================
+ Hits        12479    12481       +2     
- Misses      23774    23778       +4     

Files Changed	Coverage Δ
...Service/ApiService/onefuzzlib/notifications/Ado.cs	24.61% <11.11%> (-0.06%)	:arrow_down:
src/ApiService/ApiService/OneFuzzTypes/Model.cs	70.41% <100.00%> (+0.03%)	:arrow_up: