**What this PR does / why we need it**:
This enables deployment of write and backend modules using emptyDir in
place of a PersistentVolume for the data volume.
This is useful for Kuberenetes clusters (for example, on-prem) that are
unable to easily provide persistent volumes.
This is intended for use with something like s3 storage where (per
[comment](https://github.com/grafana/loki/blob/45b127cfd62d8dedd46b189081d4259e6416ca24/production/helm/loki/templates/backend/statefulset-backend.yaml#L30-L33)
on `persistentVolumeClaimRetentionPolicy`)
> Data on the (write or backend) nodes is easy to replace ... and will
rely on re-fetching data when needed.
**Which issue(s) this PR fixes**:
Fixes #9131
**Special notes for your reviewer**:
If there are other modules this should be applied to, please let me
know.
I'm just getting started with Loki this month and have added only the
modules which come with the default chart (gateway, read, write,
backend) and make persistent volume claims (write, backend).
**Checklist**
- [x] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [x] Documentation added
- ~Tests updated~
- no tests for modified helm modules found
- ~`CHANGELOG.md` updated~
- not used for helm changes
- ~If the change is worth mentioning in the release notes, add
`add-to-release-notes` label~
- unlikely to be noteworthy
- ~Changes that require user attention or interaction to upgrade are
documented in `docs/sources/setup/upgrade/_index.md`~
- not related to loki upgrade
- [x] For Helm chart changes bump the Helm chart version in
`production/helm/loki/Chart.yaml` and update
`production/helm/loki/CHANGELOG.md` and
`production/helm/loki/README.md`. [Example
PR](https://github.com/grafana/loki/commit/d10549e3ece02120974929894ee333d07755d213)
---------
Co-authored-by: J Stickler <[email protected]>
Co-authored-by: Michel Hollands <[email protected]>
