[cpprestsdk] Implement Enum inside Objects

[SaverioCode]

[#8937 #958(actually already closed)]
I added the support for enum type inside objects. They can be stand alone or inside vectors. Set of enums doesn't compile in favor of vectors(if necessary can be supported, if you think that set of enums are useful). Map with enums will be as before.

Other then the yaml/json from the issues I used:

{
  "openapi": "3.0.0",
  "info": {
    "title": "Enum Class Example",
    "version": "1.0.0"
  },
  "components": {
    "schemas": {
      "MyClass": {
        "type": "object",
        "properties": {
          "status": {
            	"type": "string",
		"enum": ["ACTIVE", "INACTIVE", "PENDING"]
          },
	  "test1": {
	  	"type": "array",
		"items": {
			"type": "string",
			"enum": ["available", "pending"],
			"default": "available"
		}	
	  },
	  "test2": {
		"type": "string"
	   },
	   "myMap2": {
	   	"type": "object",
		"propertyNames": {
			"type": "integer"
		},
		"additionalProperties": {
			"type": "string",
			"enum": ["PRIMO", "SECONDO", "TERZO"]
		}
	   },
	   "myMap3": {
		"type": "object",
		"propertyNames": {
			"type": "string"
		},
		"additionalProperties": {
			"type": "array",
			"items": {
				"type": "string",
				"enum": ["ARR_1", "ARR_2", "ARR_3"]
			}
		}
	   },
	   "myMap4": {
		"type": "object",
		"propertyNames": {
			"type": "string",
			"enum": ["MAP3_1", "MAP3_2", "MAP3_3"]
		},
		"additionalProperties": {
			"type": "string"
		}
	   },
	  "numVar": {
		"type": "integer",
		"format": "int32"
	  }
        }
      }
    }
  }
}

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