feat(@nestjs/swagger): New decorator ApiCallbacks

[MiguelSavignano]

PR Checklist

PR Reference nestjs/swagger#2233

• The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Docs
• Other... Please describe:

What is the new behavior?

Documentation new decorator ApiCallbacks

Does this PR introduce a breaking change?

• Yes
• No

Other information