Make track_total_hits default to false

[jpountz]

The main release highlights of Lucene 8.0 will be optimizations in the case that total hits are not needed. We could make these improvements much more visible to users by making track_total_hits default to false(instead of truetoday).

[elasticmachine]

Pinging @elastic/es-search-aggs

[jpountz]

Addressed by @jimczi via #37466.