fix spelling errors

[lenkan]

Fixing some spelling errors I've encountered when examining the API spec and source. Mostly in the openapi docs, but also some in the error messages.

[codecov]

Codecov Report

Merging #113 (02925fc) into development (e2a6b96) will not change coverage.
Report is 1 commits behind head on development.
The diff coverage is 82.35%.

@@             Coverage Diff              @@
##           development     #113   +/-   ##
============================================
  Coverage        91.83%   91.83%           
============================================
  Files               35       35           
  Lines             5596     5596           
============================================
  Hits              5139     5139           
  Misses             457      457           

Files	Coverage Δ
src/keria/app/aiding.py	86.15% <ø> (ø)
src/keria/app/grouping.py	79.76% <100.00%> (ø)
src/keria/app/notifying.py	100.00% <ø> (ø)
tests/app/test_credentialing.py	99.72% <100.00%> (ø)
tests/app/test_specing.py	100.00% <ø> (ø)
src/keria/app/credentialing.py	80.86% <85.71%> (ø)
src/keria/peer/exchanging.py	90.00% <33.33%> (ø)

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