[bitnami/seaweedfs] feat: add support for customizing PVC retention policies

This PR adds support for customizing PVC retention policies, useful for production environments.

Users can decided whether to keep or delete PVCs once they're no longer used.

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[x] Chart version bumped in Chart.yaml according to semver. This is not necessary when the changes only affect README.md files.
[x] Variables are documented in the values.yaml and added to the README.md using readme-generator-for-helm
[x] Title of the pull request follows this pattern [bitnami/] Descriptive title
[x] All commits signed off and in agreement of Developer Certificate of Origin (DCO)

bitnami / charts