Java 21 as default version

[SachinMali]

Both AEM as a Cloud Service and AEM 6.5 LTS are compatible with Java 21, and it is recommended that AEM practitioners use them. Therefore, the Archetype should use Java 21 as the default version.

Also, please note that the uber-jar of AEM 6.5 LTS (uber-jar-6.6.0) requires an API classifier like below

            <dependency>
                <groupId>com.adobe.aem</groupId>
                <artifactId>uber-jar</artifactId>
                <version>6.6.0</version>
                **<classifier>apis</classifier>**
                <scope>provided</scope>
            </dependency>

CC: @chaik @rombert