SF-3797 Add field manager field to onboarding form

[Nateowami]

This was requested to be included with the partner org is Seed Company

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This change is 

[codecov]

Codecov Report

❌ Patch coverage is 9.09091% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.02%. Comparing base (b5a2eb0) to head (8814b28).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...aft-signup-form/draft-onboarding-form.component.ts	0.00%	9 Missing ⚠️
...c/SIL.XForge.Scripture/Models/OnboardingRequest.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3863      +/-   ##
==========================================
- Coverage   81.04%   81.02%   -0.02%     
==========================================
  Files         630      630              
  Lines       40590    40601      +11     
  Branches     6588     6589       +1     
==========================================
+ Hits        32896    32897       +1     
- Misses       6661     6684      +23     
+ Partials     1033     1020      -13     

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