[BUG] Webhook PDBs are not removed after upgrading to master-head

[PhanLe1010]

To Reproduce

1. DeployLonghorn v1.4.2. Create and attach some Longhorn volumes
2. Update Longhorn to master-head. Delete all Longhorn volumes
3. Observe that longhorn-admission-webhook and longhorn-conversion-webhook PDBs are not removed

Expected behavior

Observe that longhorn-admission-webhook and longhorn-conversion-webhook PDBs are removed

[longhorn-io-github-bot]

Pre Ready-For-Testing Checklist

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

• Is there a workaround for the issue? If so, where is it documented?
  The workaround is at:

• 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:

• Have the backend code been merged (Manager, Engine, Instance Manager, BackupStore etc) (including backport-needed/*)?
  The PR is at Remove webhook PDBs in the upgrade path from v1.4.x to v1.5.0 longhorn-manager#1932

• Which areas/issues this PR might have potential impacts on?
  Area Kubernetes upgrade/Node maitainance
  Issues

• If labeled: require/LEP Has the Longhorn Enhancement Proposal PR submitted?
  The LEP PR is at

• If labeled: area/ui Has the UI issue filed or ready to be merged (including backport-needed/*)?
  The UI issue/PR is at

• If labeled: require/doc Has the necessary document PR submitted or merged (including backport-needed/*)?
  The documentation issue/PR is at

• If labeled: require/automation-e2e Has the end-to-end test plan been merged? Have QAs agreed on the automation test case? If only test case skeleton w/o implementation, have you created an implementation issue (including backport-needed/*)
  The automation skeleton PR is at
  The automation test case PR is at
  The issue of automation test case implementation is at (please create by the template)

• If labeled: require/automation-engine Has the engine integration test been merged (including backport-needed/*)?
  The engine automation PR is at

• If labeled: require/manual-test-plan Has the manual test plan been documented?
  The updated manual test plan is at

• If the fix introduces the code for backward compatibility Has a separate issue been filed with the label release/obsolete-compatibility?
  The compatibility issue is filed at

[weizhe0422]

Verified on master-head 20230601

• longhorn/longhorn-manager@6e12760

Result: PASSED

Test steps:

1. Install Longhorn V1.4.2, and create two volumes with writing some data into mount point
   
   • check that the PDBs for longhorn-admission-webhook and longhorn-conversion-webhook exist
     
2. Upgrade Longhorn to master branch build withing using kubectl apply -f https://raw.githubusercontent.com/longhorn/longhorn/master/deploy/longhorn.yaml
   • The PDBs for longhorn-admission-webhook and longhorn-conversion-webhook are gone after upgrading