Support changing the OpenAPI document based on the request

[botflux]

PR Checklist

Please check if your PR fulfills the following requirements:

• 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?

It is impossible to patch the document after it is generated and before it is served.

Issue Number: #2502

What is the new behavior?

A new option patchDocument can be passed to SwaggerModule.setup.

SwaggerModule.setup("/:tenantId/api-docs", app, document, {
  patchDocument: (req: Request, res: Response, document1: OpenAPIObject) => ({
    ...document1,
    info: {
      ...document1.info,
      title: `${req.params.tenantId}'s API document`
    }
  })
})

Does this PR introduce a breaking change?

• Yes
• [ x ] No

Other information

[kamilmysliwiec]

PR looks great! One minor thing - I'm wondering if we have any ideas other than patchDocument for the name of this function. Ideally, the name should indicate when the patching happens (on request) so it's clear to everyone that it will be called more than once (1 per request). Perhaps patchDocumentOnRequest? It's quite long, but I can't think of anything better. WDYT?

[botflux]

You are right, I'm changing it.
I think patchDocumentOnRequest is a good name.

[kamilmysliwiec]

LGTM