Consider better RuleUnit API javadoc publication

Issue description:
Since DROOLS-7212, Rule Unit API javadoc is combined with KIE API javadoc. However, if a class depends on kie-internal (e.g. DROOLS-7230 RuleConfig class), building javadoc in kie-api would require

          <additionalDependencies>
            <dependency>
              <groupId>org.kie</groupId>
              <artifactId>kie-internal</artifactId>
              <version>8.30.0.Final</version>
            </dependency>
          </additionalDependencies>

Here, 8.30.0.Final is hard-coded because ${project.version} would result in a build error because when kie-api 8.31.0.Final is built, kie-internal 8.31.0.Final doesn't exist yet.

Acceptance criteria:
Probably building Rule Unit API javadoc in drools-ruleunits and then publish separately from KIE API javadoc. (Consider if there is any better solution)