Introduce conditional index reindexing/purge

Currently, it is not possible to do operations like reindexing or index purge on only one of the message fields. This may be useful, for example, when removing an index. We are able to make Infinispan not use the index using updateIndexSchema method, however, the index data are still present in the server. We should be able to remove those.

More details: https://github.com/fax4ever/infinispan-play/pull/1#discussion_r893834600