[Feature Request] Allow the OpenSearch source plugin to shut down the Data Prepper pipeline

Is your feature request related to a problem? Please describe.
Hello! We're working on changing the opensearch-migrations tooling so our data migration implementation uses Data Prepper instead of Logstash. We will be leveraging the newly minted OpenSearch/ElasticSearch source plugin for this.

Since this is a pull-based plugin, there is a finite set of data that needs to be ingested. Once all of the data has been processed, our expectation is that the Data Prepper pipeline would shut itself down based on a signal from the source plugin. This is similar to how pull-based plugins function in Logstash.

However, Data Prepper does not currently operate this way. The pipeline/process continues to stay alive (though the source plugin is not pulling any more data) until the caller terminates it or shuts it down via APIs.

Describe the solution you'd like
Once a pull-based source plugin has completed ingesting all data, it should signal to the Data Prepper pipeline, and the pipeline should shut itself down.

Describe alternatives you've considered (Optional)
An alternative approach would be to have the pipeline / source plugin signal externally (to the caller) that all data has been processed. The caller can then invoke the Data Prepper shutdown API to stop the process.

Additional context
N/A

Start by tracing the OpenSearch/Elasticsearch source plugin's pull-based completion signal and the Data Prepper pipeline shutdown lifecycle; the issue names no files or tests. Compare the requested in-process shutdown with the alternative external signal and define which behavior should occur when all data has been ingested.