OAK-10811: (oak-search-elastic) reduce contention in IndexTracker

[fabriziofortino]

The ElasticIndexTracker has been introduced to avoid loading the index definition from the node store for each read/write into the index. The logic has been inspired by the LuceneIndexTracker.

The isUpdateNeeded has this comment:

// for Elastic, we are not interested in checking for updates on :status, index definition is enough.
// The :status gets updated every time the indexed content is changed (with properties like last_update_ts),
// removing the check on :status reduces drastically the contention between queries (that need to acquire the
// read lock) and updates (need to acquire the write lock).
// Moreover, we don't check diffs in stored index definitions since are not created for elastic.

Although the comment makes total sense, the implementation was taking into account the :status node that gets updated every time the async lane changes the index.
This creates contention because it forces the next read/write operation to recreate the IndexNode and reload the definition from the node store.

With this PR, the logic does exactly what the comment above says reducing contention and avoiding unneeded object creation.