fix(sample-gen): should return json literal example

[mathis-m]

Description

The sample gen should, in case of json media type and string literal example, try to parse the example. If it can not parse the example like the xml example shown in issue(for media type json) it will return it like it is a json string example.
In case it is parable it will return the json. This will result in rendering the json string literal examples as expected.

Motivation and Context

Fixes #6595

How Has This Been Tested?

Have taken care to ensure that literals are generated as json.

Screenshots (if appropriate):

https://editor.swagger.io/?url=https://gist.githubusercontent.com/mathis-m/20bf8fb2deabd2a5a0821418aa4adacc/raw/df18fb826d8fac8a648250dfa4e9050672992cbf/Zs2qqBv9YU.txt

Checklist

My PR contains...

• No code changes (src/ is unmodified: changes to documentation, CI, metadata, etc.)
• Dependency changes (any modification to dependencies in package.json)
• Bug fixes (non-breaking change which fixes an issue)
• Improvements (misc. changes to existing features)
• Features (non-breaking change which adds functionality)

My changes...

• are breaking changes to a public API (config options, System API, major UI change, etc).
• are breaking changes to a private API (Redux, component props, utility functions, etc.).
• are breaking changes to a developer API (npm script behavior changes, new dev system dependencies, etc).
• are not breaking changes.

Documentation

• My changes do not require a change to the project documentation.
• My changes require a change to the project documentation.
• If yes to above: I have updated the documentation accordingly.

Automated tests

• My changes can not or do not need to be tested.
• My changes can and should be tested by unit and/or integration tests.
• If yes to above: I have added tests to cover my changes.
• If yes to above: I have taken care to cover edge cases in my tests.
• All new and existing tests passed.

[tim-lai]

@mathis-m PR merged! Thanks for another contribution!

[smagafurov]

This merge breaks the schema:

openapi: 3.0.0
info:
  title: Probe
  version: 1.0.0
servers: []
components:
  schemas:
    Probe:
      type: object
      properties:
        probe:
          type: string
          example: '1.0'
paths:
  /api/v1/probe:
    post:
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Probe'
      responses:
        '200':
          description: success response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Probe'

"Example Value" incorrectly shown as:

{
  "probe": 1
}

Correctly expected as:

{
  "probe": "1.0"
}

[mathis-m]

#6872 may fix this

Fixes #6827:

https://gist.githubusercontent.com/mathis-m/6ccf292b5560fc09f50e52f2ad0f1e23/raw/f8b16efb750879d279e1c1fb3fffdb521b6dcad0/rxx6ldSupt.txt

Originally posted by @smagafurov in #6827 (comment)