This is mainly to make it possible to add other top-level configuration properties without conflicting with user-defined index names. For example, we need to introduce hibernate.search.backends.myBackend.* in Search 6, which could theoretically conflict with the configuration of an index named "backends" if we kept the current syntax.

Note: part of it was already implemented during the prototyping phase of Search 6.
Now we just need to switch from using .backend./.index. to {{.backends./.indexes. }}.