Better handling of optional dependencies

[gunnarmorling]

When building a native image with code that depends on other classes in optional dependencies, a NoClassDefFoundError is raised. This makes sense but it's hard to fix by the application developer, as they will have to find out which dependency contains the missing class(es) and add them. Some support by Quarkus would be desirable, e.g. it could analyse any optional dependencies of the dependencies used in the native build so it can produce a message such as "class x.y.z couldn't be found but it's located in JAR with GAV abc. Consider to add it as a provided dependency".

[dmlloyd]

We might consider something like the allow-incomplete-classpath feature of GraalVM but limited in scope to just declared optional dependencies.

[knuspertante]

I think oracle/graal#4661 could help here as mentioned in #25526.