feat(swagger): JSON and YAML document endpoints customizable

[jcolladosp]

PR Checklist

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

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
• CI related changes
• Other... Please describe:

What is the current behavior?

Right now the swagger json and yam are deployed in ${finalPath}-json and ${finalPath}-yaml, without possibility of customization:

http://localhost:3000/api-json
http://localhost:3000/api-yaml

Issue Number: #1968

What is the new behavior?

Added the options jsonDocumentUrl and yamlDocumentUrl in the interface SwaggerCustomOptions
If the option value is present, json and/or yaml documents are served in the specified url.
Furthermore, if globalPrefix is specified in the nest options, it's used as prefix for the custom urls.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[jmcdo29]

LGTM

[kamilmysliwiec]

Apologies for not looking at this PR sooner. There are some merge conflicts, if you could take a look & resolve them that would be great

[jcolladosp]

Hi @kamilmysliwiec, since I deleted the head repository by mistake, I just opened a new PR with the same changes and without the conflicts:
#2273

Thanks