Introduce strong typed indexing configuration

<!-- Minimal -->
<indexing>
    <indexed-entities>
        <indexed-entity>org.infinispan.query.test.Person</indexed-entity>
    </indexed-entities>
</indexing>

<!-- Medium -->
<indexing storage="file" path="${server.data}/index">
    <indexed-entities>
        <indexed-entity>org.infinispan.query.test.Person</indexed-entity>
    </indexed-entities>
</indexing>

<indexing storage="heap">
    <indexed-entities>
        <indexed-entity>org.infinispan.query.test.Person</indexed-entity>
    </indexed-entities>
</indexing>

<!-- Maximal -->
<indexing storage="file" path="${server.data}/index">
    <index-reader refresh-interval="10s"/>
    <!-- Check SYNC behavior Hsearch 6 -->
    <index-writer mode="async" commit-internal="10s"/>
    <indexed-entities>
        <indexed-entity>org.infinispan.query.test.Person</indexed-entity>
    </indexed-entities>
    <properties>
	<property name="default.indexwriter.merge_factor">30</property>
    </properties>
</indexing>