feat(decorator): @ApiResponse annotation, support multiple response body examples

[slowquery]

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)

I couldn't find the CHANGELOG.md file
If you guide me, I will edit the document.

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] 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?

I would like to document and expose multiple response situations for the same http response status code.
It is supported in openapi 3.0.0, and the 'examples' key in the response content has been modified to be usable.

Issue Number: N/A

What is the new behavior?

Support for optional examples key for @ApiResponse annotation
- support to show multiple response body examples in one response code.

Does this PR introduce a breaking change?

[x] Yes (i think yes.)
[ ] No

Other information

I added one simple test case.

[slowquery]

I am modifying the e2e test.

[slowquery]

I modified the test to work normally.

[slowquery]

Is there any problem in applying the 'examples' support I have suggested?
I want to get feedback.