KNN overwrite the query while it's not expected

[donhardman]

When we use the code

$client->index('test')->search("query term")->knn(...)

we expect to perform a hybrid search that combines vector and keyword searches.

However, due to the current implementation, we can't do this without directly manipulating internal classes to build our query.

I suggest we consider an approach where using knn extends the current query rather than altering it. If we need to make changes, we can always use the reset method.

[sanikolaev]

To make things clear, here's what it looks like in the JSON DSL https://manual.manticoresearch.com/dev/Searching/KNN?client=JSON#Filtering-KNN-vector-search-results

[Nick-S-2018]

Done in https://github.com/manticoresoftware/manticoresearch-php/commit/6fbdaacd80a4ec82a51a66d72ce9c5f546c7ef69