[BUG][JAVA] AbstractOpenApiSchema package output and declaration missmatch

Created by: BenjaminKlatt

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

The class AbstractOpenApiSchema is generated into the model package but declares a model package within the invoker package

Not sure if you prefer a pull request over a bug report. so starting with a bug report and a suggested fix below,

openapi-generator version

openapi-generator-maven-plugin 5.0.0

OpenAPI declaration file content or url

Does not depend on a specific openapi spec

Generation Details

Maven Plugin Configuration

<plugin>
	<groupId>org.openapitools</groupId>
	<artifactId>openapi-generator-maven-plugin</artifactId>
	<version>5.0.0</version>
	<executions>
		<execution>
			<goals>
				<goal>generate</goal>
			</goals>
			<configuration>
				<generatorName>java</generatorName>
				<inputSpec>${openapi.spec.path}</inputSpec>
				<apiPackage>com.example.api</apiPackage>
				<invokerPackage>com.example.invoker</invokerPackage>
				<modelPackage>com.example.model</modelPackage>
				<configOptions>
					<library>native</library>
					<dateLibrary>java8</dateLibrary>
				</configOptions>
			</configuration>
		</execution>
	</executions>
</plugin>

Steps to reproduce

1. add plugin definition above to a maven project's pom
2. reference any json based openapi spec as ${openapi.spec.path} property
3. run mvn mvn clean generate-sources
4. check AbstractOpenApiSchema.java file for valid package declaration (is generated into com.example.model but declares com.example.invoker.model as package

Related issues/PRs

Suggest a fix

Depending the result expected, the mustach template should use the model package declaration instead of {{invokerPackage}}.model https://github.com/OpenAPITools/openapi-generator/blob/edf153eedef58bd04ffa02a56ecbe60a7165bf0f/modules/openapi-generator/src/main/resources/Java/libraries/native/AbstractOpenApiSchema.mustache#L3 as this is also the case in the native petstore example: https://github.com/OpenAPITools/openapi-generator/blob/edf153eedef58bd04ffa02a56ecbe60a7165bf0f/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/AbstractOpenApiSchema.java