Slow query filter method added

[MishukAdhikari]

To filter slow query it looks like

Telescope::filter(function (IncomingEntry $entry) {

    return $entry->type === EntryType::QUERY && ($entry->content['slow'] ?? false);

});

If we use method it's much more readable and easy to add multiple or

Telescope::filter(function (IncomingEntry $entry) { 
    return $entry->isSlowQuery();
});