**What this PR does / why we need it**:
Support Azure Blob Storage in helm chart. See
https://grafana.com/docs/loki/latest/storage/#azure-storage-account-1

**Which issue(s) this PR fixes**:


**Special notes for your reviewer**:

**Checklist**
- [ ] Reviewed the `CONTRIBUTING.md` guide
- [x] Documentation added
- [ ] Tests updated
- [x] `CHANGELOG.md` updated
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/upgrading/_index.md`

Signed-off-by: Jan-Otto Kröpke <jok@cloudeteer.de>