Clean before building javadocs, because third-party-jackson-core's mvn package is not idempotent. (#2607)
Clean before building javadocs, because third-party-jackson-core's mvn package is not idempotent. (#2607)

This fixes an error where release-javadoc.yml fails with "Error creating shaded jar: duplicate
entry: META-INF/services/software.amazon.awssdk.thirdparty.jackson.core.JsonFactory"
aws/aws-sdk-java-v2,aws/aws-sdk-java-v2,aws/aws-sdk-java-v2,aws/aws-sdk-java-v2,aws/aws-sdk-java-v2