docs: Updated Fluent Bit docs to use official plugin + Sandbox (backport release-3.0.x)

[loki-gh-app]

Backport 3e451c7 from #14004

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We now recommend using the official Fluent Bit plugin since the Fluent Bit community actively maintains it and is now more feature-rich than the community plugin. The update:

• Moved community plugin to its own page for users still using the community plugin
• Updated _index to give examples using the official fluent bit plugin
• Added interactive sandbox

Sandbox preview for testing: https://killercoda.com/grafana-dev-testing/course/loki/fluentbit-loki-tutorial

Note link to the sandbox will fail in docs will fail with a 404 since we have not pushed the sandbox to production

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