### What changes were proposed in this pull request?
This PR is a giant plumbing PR that plumbs an `ExecutorDecommissionInfo` along
with the DecommissionExecutor message.
### Why are the changes needed?
The primary motivation is to know whether a decommissioned executor
would also be loosing shuffle files -- and thus it is important to know
whether the host would also be decommissioned.
In the absence of this PR, the existing code assumes that decommissioning an executor does not loose the whole host with it, and thus does not clear the shuffle state if external shuffle service is enabled. While this may hold in some cases (like K8s decommissioning an executor pod, or YARN container preemption), it does not hold in others like when the cluster is managed by a Standalone Scheduler (Master). This is similar to the existing `workerLost` field in the `ExecutorProcessLost` message.
In the future, this `ExecutorDecommissionInfo` can be embellished for
knowing how long the executor has to live for scenarios like Cloud spot
kills (or Yarn preemption) and the like.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
Tweaked an existing unit test in `AppClientSuite`
Closes#29032 from agrawaldevesh/plumb_decom_info.
Authored-by: Devesh Agrawal <devesh.agrawal@gmail.com>
Signed-off-by: Holden Karau <hkarau@apple.com>
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