[BUG] [JAVA-UNDERTOW] integer enum generates value of type string

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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When generating classes from the specified openapi.yaml specification which contains enums of type integer, the generated code has incorrect type for values

openapi-generator version

5.0.1 version of openapi-generator-maven-plugin

openapi-version

3.0.0

OpenAPI declaration file content or url

QualificationFragment:
      description: qualification of the resource instance
      type: object
      properties:
        name:
          type: string
          example: "Undertowtest instance 1"
        type:
          type: integer
          enum:
            - 1
            - 2

Generation Details

                    <plugin>
                        <groupId>org.openapitools</groupId>
                        <artifactId>openapi-generator-maven-plugin</artifactId>
                        <version>${openapigen.version}</version>
                        <executions>
                            <execution>
                                <goals>
                                    <goal>generate</goal>
                                </goals>
                                <configuration>
                                    <inputSpec>${project.basedir}/openapi.yaml</inputSpec>
                                    <generatorName>org.openapitools.codegen.languages.JavaUndertowServerCodegen</generatorName>
                                    <modelPackage>com.api.model</modelPackage>
                                    <apiPackage>com.api</apiPackage>
                                </configuration>
                            </execution>
                        </executions>
                    </plugin>
                </plugins>

Clarity in explaining the issue

The generated code generates the following output when enum of type integer is used

public class QualificationFragment   {
  
  private String name;


  public enum TypeEnum {
    NUMBER_1(1),
    NUMBER_2(2);

    private String value;

    TypeEnum(String value) {
      this.value = value;
    }

    @Override
    @JsonValue
    public String toString() {
      return value;
    }
  }

  private TypeEnum type;

  /**
   */
  public QualificationFragment name(String name) {
    this.name = name;
    return this;
  }

  
  @ApiModelProperty(example = "Undertowtest instance 1", value = "")
  @JsonProperty("name")
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }

  /**
   */
  public QualificationFragment type(TypeEnum type) {
    this.type = type;
    return this;
  }

  
  @ApiModelProperty(value = "")
  @JsonProperty("type")
  public TypeEnum getType() {
    return type;
  }
  public void setType(TypeEnum type) {
    this.type = type;
  }
}

Steps to reproduce

1. Generate code with a yaml spec that has integer type enum specifications

Related issues/PRs

Suggest a fix

Start with the JavaUndertowServerCodegen generator and the provided OpenAPI YAML, then reproduce the output through the openapi-generator-maven-plugin. Compare the generated integer enum declaration with the expected numeric value type; done means the generated Undertow model preserves integer enum values instead of declaring them as String.