fix(): move modifiers properties to items object on array type

[nartc]

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?

[x] 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?

Array type under parameters has its items' modifiers on the same level as items where those modifiers should be children of items

parameters:
   formatArray:
      type: 'array'
      format: 'uuid'
      items:
         type: string

Issue Number: #1391

What is the new behavior?

Modifiers are now moved inside of items

parameters:
   formatArray:
      type: 'array'
-     format: 'uuid'
      items:
         type: string
+        format: 'uuid'

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information