### What changes were proposed in this pull request?
This PR proposes to register the executor source with the Spark metrics system when running in local mode.
### Why are the changes needed?
The Apache Spark metrics system provides many useful insights on the Spark workload.
In particular, the [executor source metrics](https://github.com/apache/spark/blob/master/docs/monitoring.md#component-instance--executor) provide detailed info, including the number of active tasks, I/O metrics, and several task metrics details. The executor source metrics, contrary to other sources (for example ExecutorMetrics source), is not available when running in local mode.
Having executor metrics in local mode can be useful when testing and troubleshooting Spark workloads in a development environment. The metrics can be fed to a dashboard to see the evolution of resource usage and can be used to troubleshoot performance,
as [in this example](https://github.com/cerndb/spark-dashboard).
Currently users will have to deploy on a cluster to be able to collect executor source metrics, while the possibility of having them in local mode is handy for testing.
### Does this PR introduce _any_ user-facing change?
- This PR exposes executor source metrics data when running in local mode.
### How was this patch tested?
- Manually tested by running in local mode and inspecting the metrics listed in http://localhost:4040/metrics/json/
- Also added a test in `SourceConfigSuite`
Closes#28528 from LucaCanali/metricsWithLocalMode.
Authored-by: Luca Canali <luca.canali@cern.ch>
Signed-off-by: Thomas Graves <tgraves@apache.org>
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