[Java] Add a Jandex index to microprofile client packages

Created by: languitar

Quarkus, as one potential target for using the Java microprofile client generator, requires a Jandex index to be present in library jars for discovering beans inside these jars. Therefore, include Jandex index generation in the pom.xml for microprofile clients as explained here: https://quarkus.io/guides/cdi-reference#how-to-generate-a-jandex-index

Generating and shipping the index is only a small overhead that is probably not worth an additional client option.

Considering a backport to 5.2 or 5.1 would be great.

CC @bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608 @nmuesch

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