[Rust Server] Support complex query parameters

[richardwhiuk]

Support complex query parameters by using the correct FromStr implementation and using ToString at all.

This enables support for definitions such as:

      parameters:
        - name: list-of-strings
          in: query
          schema:
            type: array
            items:
              $ref: '#/components/schemas/StringObject'

This fix was contributed by @mirw and reviewed by myself on behalf of @Metaswitch.

Rust Server Technical Committee

• @frol
• @farcaller
• @bjgill

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