[IMPROVEMENT] Record instance-manager name for a block disksin node.spec.diskStatus

[derekbit]

Is your improvement request related to a feature? Please describe (👍 if you like this request)

This is an improvement as well as a subtask of #6001.

For a block-type disk, which is managed by an instance-manager pod (specifically, the spdk_tgt component), the proposed improvement is to record the name of the instance-manager pod that is currently managing the disk in the node.spec.diskStatus[i].instanceManagerName field. This information will help identify which instance-manager pod is responsible for a particular disk and determine if the disk is already is transferred to a new instance-manager during upgrade.

For a filesystem-type disk, the node.spec.diskStatus[i].instanceManagerName field is left empty because this type of disk is not exclusively managed by any instance-manager.

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Additional context

[longhorn-io-github-bot]

Pre Ready-For-Testing Checklist

• Where is the reproduce steps/test steps documented?
  The reproduce steps/test steps are at:

1. Create a Longhorn cluster and enable v1 and v2 data engines.
2. Add filesystem-type and block-type disks
3. Check filesystem-type's diskStatus.instanceManagerName is empty
4. Check block-types's diskStatus.instanceManagerName is the running instance-manager.

• Does the PR include the explanation for the fix or the feature?

• Does the PR include deployment change (YAML/Chart)? If so, where are the PRs for both YAML file and Chart?
  The PR for the YAML change is at:
  The PR for the chart change is at:

#8460

• Have the backend code been merged (Manager, Engine, Instance Manager, BackupStore etc) (including backport-needed/*)?
  The PR is at

longhorn/longhorn-manager#2761

• Which areas/issues this PR might have potential impacts on?
  Area: disk management, instance-manager
  Issues