Support remote location for last_run_metadata_path

[Flixi555]

Tracking the sql_last_value via the last_run_metadata_path parameter is tricky in a containerized Logstash setup unless some form of persistent storage is attached to the container, which in turn brings its own challenges and is simply not always possible to implement.

Allowing for remote locations of the stored metadata would make tracking the state possible in stateless instances of Logstash. I'm not exactly sure how this is best accomplished, but the first idea would be to store it in Elasticsearch.