Allow configuring Elastic Timeout

[cypressious]

The Elastic client allows configuring request timeouts via ConnectionSettings.RequestTimeout, however this is not exposed in AspNetCore.HealthChecks.Elasticsearch.

Consider adding a way to configure the timeout.

[unaizorrilla]

PR welcome ! :-)

[inkel]

I'm happy to send a PR for this, however, I've got a couple of questions:

Both current extensions IHealthChecksBuilder.AddElasticsearch accept an optional, last parameter TimeSpan? timeout = default. Now, according to the documentation, this parameter is An optional System.TimeSpan representing the timeout of the check.

My question would be: should we use that value too and pass it to ElasticsearchOptions or should we add a new one TimeSpan? requestTimeout = default?