[BUG] Understanding what caused a pipeline shutdown can be difficult.

Describe the bug

Sometimes Data Prepper shuts down without a clear reason as to why.

2024-01-18T06:23:32.523 [pool-33-thread-1] INFO    org.opensearch.dataprepper.DataPrepper - Shutting down pipeline: my-pipeline
2024-01-18T06:23:32.524 [pool-33-thread-1] INFO  org.opensearch.dataprepper.pipeline.Pipeline - Pipeline [my-pipeline] - Received shutdown signal with buffer drain timeout PT0S, processor shutdown timeout PT5M, and sink shutdown timeout PT30S. Initiating the shutdown process
2024-01-18T06:23:34.564 [pool-33-thread-1] INFO  org.opensearch.dataprepper.plugins.source.loghttp.HTTPSource - Stopped http source.

Expected behavior

I'd like to see clearer logging when the pipeline shuts down. Flor example, was it from a call to POST /shutdown?

Environment (please complete the following information):

• Data Prepper: 2.6.1