Support adding Vendor Extensions to Infos

[fmauNeko]

Hello,

This is a PR allowing the addition of Vendor Extensions to the info object.
This is useful for ReDoc, to add a logo on the documentation pages, as an example.

Feel free to tell me if anything should be changed !

[codecov]

Codecov Report

Merging #1215 into master will decrease coverage by <.01%.
The diff coverage is 60%.

@@            Coverage Diff             @@
##           master    #1215      +/-   ##
==========================================
- Coverage   67.45%   67.44%   -0.01%     
==========================================
  Files          28       28              
  Lines        7783     7797      +14     
==========================================
+ Hits         5250     5259       +9     
- Misses       2047     2050       +3     
- Partials      486      488       +2

Impacted Files	Coverage Δ
scan/scanner.go	68.86% <ø> (ø)	⬆️
scan/meta.go	74.23% <60%> (-1.61%)	⬇️
generator/structs.go	46.25% <0%> (+1.25%)	⬆️

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