Add support for enum in object params

Feature request

It should be possible to use enum in parameters of type object on string fields.

Use case

An example of usage would be:

    params:
    - name: go
      description: >-
        Golang options, such as flags, …
      type: object
      properties:
        version:
          type: string
          enum: ["1.19", "1.20", "1.21", "1.22"]
        GOFLAGS: {type: string}
        GOOS: {type: string}
        GOARCH: {type: string}
        CGO_ENABLED: {type: string}
      default:
        version: "1.21"
        GOFLAGS: "-v"
        GOOS: ""
        GOARCH: ""
        CGO_ENABLED: "0"