Fix generation of default array values for kotlin client

Created by: Rattenkrieg

Additional fixes for #10865 (closed)

Currently, a request containing default value for an array would break kotlin generation yielding java.lang.ClassCastException

java.lang.String cannot be cast to com.fasterxml.jackson.databind.node.ArrayNode

The problem lies in swagger dependency that doesn't handle default values for arrays as java arrays rather passing it as string like ["value1"]. This is the line that feeds string value to our schema. Simple spec below works fine reproducing the issue. In this PR I decided to skip such string values as I don't see jackson parser being wired in AbstractKotlinCodegen, however if maintainers decide that parsing such strings is really something nice to have, I could hack on this PR further.

  /foo/bar:
    post:
      operationId: UpdateBar
      consumes:
        - multipart/form-data
      parameters:
        - name: values
          in: formData
          required: false
          type: array
          items:
            type: string
            enum:
              - value1
              - value2
          default:
            - value1
    responses:
        "200":
          description: "Success."

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