feat: allow cloning home-pvc from custom dataSource

[joshuasimon-taulia]

What does this PR do?

Add the ability to clone the home PVC from an existing volume, GCP snapshot, etc as described in CSI Volume Cloning. Not only is this useful for CI/testing against the jenkins chart, this can also be used to restore from a backup or to facilitate a major jenkins version upgrade.

If you modified files in the ./charts/jenkins/ directory, please also include the following:

Submitter checklist

Beta Give feedback

1. I bumped the "version" key in ./charts/jenkins/Chart.yml.
2. I added a new changelog entry to ./charts/jenkins/CHANGELOG.md.
3. I followed the technical requirements.

Special notes for your reviewer

i added tests

[joshuasimon-taulia]

https://github.com/jenkinsci/helm-charts/actions/runs/5686349589/job/15412972064?pr=899

Retrieving https://api.github.com/repos/quintush/helm-unittest/releases/tags/v0.2.11
No download_url found only searching for linux
Downloading  to location /tmp/_dist/
curl: Remote file name has no length!
curl: (23) Failed writing received data to disk/application
Failed to install helm-unittest
Error: plugin install hook for "unittest" exited with error
For support, go to https://github.com/kubernetes/helm
Error: Process completed with exit code 1.

this probably needs to be updated to the upstream https://github.com/helm-unittest/helm-unittest/releases/tag/v0.2.11. @timja @NotMyFault mind re-running/having alook?