Improve redirect detection for javadocs

### New feature, improvement proposal

Currently the given `externalJavadocBaseUrl` is being used first to construct a target url (e.g. to `element-list`) and then it is requested. This fails when there is no deep redirect support. For example the Oracle URL redirects to but is also redirected to instead of .

In order to support redirects which always redirect to the index page, the request url should be constructed *after* the redirect target has been been resolved.

This requires some change in https://github.com/apache/maven-plugin-tools/blob/4ee91b1f88c6ab02323be397f45e978ebc1064c0/maven-plugin-tools-api/src/main/java/org/apache/maven/tools/plugin/javadoc/JavadocSite.java#L539.