[BUG][Spring] Enum value is ignored for path and query params

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

When a path or query param has enum constraint, it is generated as String.
We need to generate it as an enum.

openapi-generator version

Last from master

OpenAPI declaration file content or url

---
openapi: "3.0.1"
info:
  title: "My Little Pony"
  description: "Friendship is magic"
  contact: {}
  version: "1.0.0"
paths:
  /ponies:
    summary: "Everything for ponies"
    get:
      summary: "List"
      operationId: "list"
      parameters:
        - name: "name"
          in: "query"
          required: false
          schema:
            type: "string"
            enum:
              - "Big McIntosh"
              - "Rainbow Dash"
              - "Pinkie Pie"
              - "Rarity"
      responses:
        200:
          description: "Status 200"
          content:
            application/json:
              schema:
                type: "array"
                items:
                  $ref: "#/components/schemas/Pony"
        400:
          description: "Status 400"
components:
  schemas:
    Pony:
      type: "object"
      properties:
        Id:
          type: "string"

Generation Details

Spring generator with spring-boot library
https://github.com/OpenAPITools/openapi-generator/blob/master/bin/configs/spring-boot-delegate.yaml

Steps to reproduce

Related issues/PRs

Suggest a fix

Start with the Spring spring-boot generator configuration at bin/configs/spring-boot-delegate.yaml and the supplied OpenAPI declaration. Inspect how its path and query parameters are generated, then compare the enum parameter output with the expected enum type; done means enum-constrained parameters are no longer generated as String.