Calculate total duration of Index Sanitization

It would be great to have the total amount of time which has been consumed to check the validity of lucene indexes.

Therefor the log statement in [1] ff should be extended to display also the accumulated time (in seconds) spend in this validation. In that case the latest log statement contains the total amount of time spent there.

[1] https://github.com/apache/jackrabbit-oak/blob/bcab8d29511775c31218f780735939f7faf1c6b7/oak-lucene/src/main/java/org/apache/jackrabbit/oak/plugins/index/lucene/directory/IndexSanityChecker.java#L67