feat: document args/options schemas, fixes #157

[danielgtaylor]

Since the built-in --help generator only gives a name of each argument and a short text description of each option, this PR adds schema information for both to the generated description. There are two groups: 1. path parameter arguments and 2. query param / header arguments. Each is rendered as an object where the keys are the parameter name and the schema for each is shown next to it, similar to how the request/response body schemas work.

To take the example in #157, it now produces this to describe the image type argument:

[codecov]

Codecov Report

Merging #212 (6b1980e) into main (6b9ecae) will increase coverage by 0.12%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #212      +/-   ##
==========================================
+ Coverage   75.63%   75.76%   +0.12%     
==========================================
  Files          26       26              
  Lines        3555     3574      +19     
==========================================
+ Hits         2689     2708      +19     
  Misses        666      666              
  Partials      200      200              

Files Changed	Coverage Δ
openapi/openapi.go	88.48% <100.00%> (+0.56%)	⬆️

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