Update Mimir documentation, Agent-->Alloy

[clayton-cornell]

This issue tracks the work for updating Agent-->Alloy in the Mimir documentation.

### Tasks
- [ ] Identify the topics that reference or document using Agent with Alloy
- [ ] Assess the contents for minor update, rewrite, or remove.

[clayton-cornell]

Initial scan of Mimir docs shows multiple hits on Agent in these topics:

• [ ] helm-charts/mimir-distributed/run-production-environment-with-helm/monitor-system-health.md
• [ ] helm-charts/mimir-distributed/run-production-environment-with-helm/_index.md
• [ ] helm-charts/mimir-distributed/get-started-helm-charts/_index.md
• [ ] mimir/configure/configure-native-histograms-ingestion.md
• [ ] mimir/set-up/migrate/migrate-from-thanos-to-mimir-with-thanos-sidecar.md
• [ ] mimir/release-notes/v2.2.md
• [ ] mimir/manage/monitor-grafana-mimir/collecting-metrics-and-logs.md
• [ ] mimir/references/architecture/components/distributor.md
• [ ] mimir/get-started/_index.md
• [ ] mimir/send/_index.md
• [ ] mimir/send/native-histograms/_index.md

[clayton-cornell]

Log output shows these links into Agent docs from Mimir (overlaps the previous info, including here for completeness)

WARN  /docs/mimir/latest/get-started/: [render-link] page links to the Grafana Cloud Agent page /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/.
WARN  /docs/mimir/next/get-started/: [render-link] page links to the Grafana Cloud Agent page /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/.
WARN  /docs/mimir/v2.12.x/get-started/: [render-link] page links to the Grafana Cloud Agent page /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/.

[clayton-cornell]

/docs/mimir/latest/get-started/ -> /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/. /docs/mimir/next/get-started/ -> /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/. /docs/mimir/v2.0.x/operators-guide/getting-started/ -> /docs/grafana-cloud/agent/#installing-the-grafana-agent. /docs/mimir/v2.1.x/operators-guide/getting-started/ -> /docs/grafana-cloud/agent/#installing-the-grafana-agent. /docs/mimir/v2.10.x/get-started/ -> /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/. /docs/mimir/v2.11.x/get-started/ -> /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/. /docs/mimir/v2.12.x/get-started/ -> /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/. /docs/mimir/v2.2.x/operators-guide/getting-started/ -> /docs/grafana-cloud/agent/#installing-the-grafana-agent. /docs/mimir/v2.3.x/operators-guide/get-started/ -> /docs/grafana-cloud/agent/#installing-the-grafana-agent. /docs/mimir/v2.4.x/operators-guide/get-started/ -> /docs/grafana-cloud/agent/#installing-the-grafana-agent. /docs/mimir/v2.5.x/operators-guide/get-started/ -> /docs/grafana-cloud/agent/#installing-the-grafana-agent. /docs/mimir/v2.6.x/operators-guide/get-started/ -> /docs/grafana-cloud/agent/#installing-the-grafana-agent. /docs/mimir/v2.7.x/operators-guide/get-started/ -> /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/. /docs/mimir/v2.8.x/get-started/ -> /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/. /docs/mimir/v2.9.x/get-started/ -> /docs/grafana-cloud/monitor-infrastructure/integrations/agent/flow/setup/install/.