Document application class loading search order for common libraries

For design issue: https://github.ibm.com/websphere/WS-CD-Open/issues/34217

Update topic https://openliberty.io/docs/latest/class-loader-library-config.html#_configure_global_libraries to mention the content of common libraries is searched in the order in which libraries appear in the the application class loader's commonLibraryRefs configuration.

The update enables users to understand this seemingly internal server behavior is both reliable and supported.

todo: define actual content change

Template questions
Q: What do 80% of target users need to know to be most easily productive using your runtime update?

There is no corresponding runtime update. That said, target users must understand their application's dependencies on common library content in order to prescribe the order in which these libraries are searched.

Q: Which release will the runtime updates target? The Open Liberty docs team will aim to get the docs updates published in sync with the runtime updates.

N/A: There is no corresponding runtime update.