Support charset information on swagger2 data import (#5781)

[89ht]

changelog(Fixes): Fixed and issue where request body data was not properly set if charset information is set in "consumes" field for Swagger files

Closes #5781

[filfreire]

LGTM.

Used example swagger provided by @89ht

{
  "swagger": "2.0",
  "info": {
    "title": "My API",
    "version": "1.0.0"
  },
  "consumes": [
    "application/json; charset=utf-8"
  ],
  "produces": [
    "application/json; charset=utf-8"
  ],
  "paths": {
    "/users": {
      "post": {
        "summary": "Create a new user",
        "description": "Creates a new user with the specified data",
        "parameters": [
          {
            "name": "user",
            "in": "body",
            "description": "The user data",
            "required": true,
            "schema": {
              "$ref": "#/definitions/User"
            }
          }
        ],
        "responses": {
          "200": {
            "description": "User created successfully"
          }
        }
      }
    }
  },
  "definitions": {
    "User": {
      "type": "object",
      "properties": {
        "id": {
          "type": "integer"
        },
        "name": {
          "type": "string"
        }
      }
    }
  }
}

[filfreire]

@89ht you can claim a free tshirt for this PR contribution - find more at https://konghq.com/community/open-source-contribution