### What changes were proposed in this pull request?
Rename `spark.worker.decommission.enabled` to `spark.decommission.enabled` and move it from `org.apache.spark.internal.config.Worker` to `org.apache.spark.internal.config.package`.
### Why are the changes needed?
Decommission has been supported in Standalone and k8s yet and may be supported in Yarn(https://github.com/apache/spark/pull/27636) in the future. Therefore, the switch configuration should have the highest hierarchy rather than belongs to Standalone's Worker. In other words, it should be independent of the cluster managers.
### Does this PR introduce _any_ user-facing change?
No, as the decommission feature hasn't been released.
### How was this patch tested?
Pass existed tests.
Closes#29466 from Ngone51/fix-decom-conf.
Authored-by: yi.wu <yi.wu@databricks.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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