chore: [release-3.0.x] docs: Updated bucket names and added warning

[grafanabot]

Backport 86fbfff from #13347

---

Fixed the naming convention for buckets within docs and added a warning linking to this security post:
https://grafana.com/blog/2024/06/27/grafana-security-update-grafana-loki-and-unintended-data-write-attempts-to-amazon-s3-buckets/

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• 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
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR