dateLibrary java8 does works now with xml (#8444)

Co-authored-by: v.bychkov <v.bychkov@betterbits.de>

modules/openapi-generator/src/main/resources/Java/libraries/resteasy/pom.mustache

@@ -239,6 +239,11 @@
             <artifactId>jackson-dataformat-xml</artifactId>
             <version>${jackson-version}</version>
         </dependency>
+        <dependency>
+            <groupId>io.github.threeten-jaxb</groupId>
+            <artifactId>threeten-jaxb-core</artifactId>
+            <version>1.2</version>
+        </dependency>
 
         {{/withXml}}
         <dependency>

modules/openapi-generator/src/main/resources/Java/model.mustache

@@ -26,6 +26,8 @@ import com.fasterxml.jackson.annotation.JsonCreator;
 {{/jackson}}
 {{#withXml}}
 import javax.xml.bind.annotation.*;
+import javax.xml.bind.annotation.adapters.*;
+import io.github.threetenjaxb.core.*;
 {{/withXml}}
 {{#jsonb}}
 import java.lang.reflect.Type;

modules/openapi-generator/src/main/resources/Java/pojo.mustache

@@ -59,6 +59,9 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
   @XmlElementWrapper({{#xmlNamespace}}namespace="{{.}}", {{/xmlNamespace}}name = "{{xmlName}}{{^xmlName}}{{baseName}}{{/xmlName}}")
       {{/isXmlWrapped}}
     {{/isContainer}}
+  {{#isDateTime}}
+  @XmlJavaTypeAdapter(OffsetDateTimeXmlAdapter.class)
+  {{/isDateTime}}
   {{/isXmlAttribute}}
   {{/withXml}}
   {{#gson}}