chore: [release-3.0.x] docs: Update Get-Started Labels

[grafanabot]

Backport a08ee68 from #13188

---

docs: Update Get-Started Labels

Description

The current section on "Getting Started with Labels" provides several YAML configuration examples. For newcomers, it is not immediately clear that these examples pertain to configurations for log collectors like Promtail/Alloy, rather than Loki itself. This can lead to confusion about where and how to apply these configurations. Clarifying this in the documentation will enhance its accessibility and usability, particularly for those new to Loki and its ecosystem.

Proposed Change

Add a brief note at the beginning of the section clarifying that these examples are meant for log collector configurations, such as Promtail/Alloy.

Issue(s) this PR fixes

Fixes: #13187

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