Ping will only allow to return healthy or unhealthy statuses. By using
Elasticsearch Cluster Health API [1] we can also return degraded if
the cluster is in yellow state.

Note that I needed to convert the cluster status to a string instead
of using Elasticsearch.Net.Health enum, as otherwise we would need to
add a reference to the Elasticsearch.Net NuGet package.

1: https://www.elastic.co/guide/en/elasticsearch/reference/current/cluster-health.html

By default the option is false, meaning it will use ping as it was
previously doing. If the user wants advanced health check they can
call this method which will instruct ElasticsearchHealthCheck to use
the Cluster Health API instead. See parent commit for more information.

These new tests don't need a running Elasticsearch instance but rather
create a mock HTTP server that will send back responses in the same
format as Elasticsearch Cluster Health API does.

This was for debugging purposes.

Do not unnecessarily assigned a default value that's equal to the zero value of a boolean.

Co-Authored-By: Ivan Maximov <sungam3r@yandex.ru>