Add withTrackTotalHits method to Builder class to add track_total_hits

[caufab]

Add withTrackTotalHits method to Builder class to add track_total_hits in elasticsearch request body

[pdphilip]

Thanks for the PR @caufab - please provide more details (and use cases) around the utility of adding this as a feature

[caufab]

@pdphilip I was searching a way to add the flag track_total_hits in the body of the search request (outside the query field).
As explained in the official ES documentation, setting this param to true will allow to count the total number of elements found (see EDIT) in the whole index. Without this, if the index contains lots of hits (more than 10.000) hits field will contain always 10000.
This method can be called via the builder when creating the query very easily, like the example below:

$builder = Product::query();
$builder->trackTotalHits();

// build the query
$builder->search('test search');
$builder->whereTerm ....

// run the query
$results = $builder->get();

Of course the total hits will be in the same hits field as without the trackTotalHits, so we will need to take them in them meta data, but the count is precise, not limited to 10k.

EDIT: to be precise, not the total number of elements found, actually the total number of elements that have a hit with that query in the whole index