**What this PR does / why we need it**:
It adds missing HPA (HorizontalPodAutoscaler) templates to write, read,
and backend components
**Which issue(s) this PR fixes**:
Fixes #7864

**Checklist**
- [x] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [x] Documentation added
- [ ] Tests updated
- [x] `CHANGELOG.md` updated
- [x] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/upgrading/_index.md`

Co-authored-by: Oleksii Boiko <oleksii_boiko@external.mckinsey.com>