feat: stronger openapi definitions for long running operations

[Sotatek-Patrick-Vu]

Relevant signify-ts here WebOfTrust/signify-ts#363

[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.74%. Comparing base (e669b39) to head (4e954a0).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/keria/core/longrunning.py	69.66%	27 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #420      +/-   ##
==========================================
+ Coverage   86.97%   87.74%   +0.76%     
==========================================
  Files          25       26       +1     
  Lines        5460     5808     +348     
==========================================
+ Hits         4749     5096     +347     
- Misses        711      712       +1     

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