feat: update observability documentation

[caalador]

Move old documentation under v4
Add migration documentation
and update references, configuration
and customization documents.

[github-actions]

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URL: https://docs-preview-pr-5769.fly.dev

Changed pages

Added content is highlighted in green; removed content is marked in red on each page.

• tools/observability — modified, +8/-5 lines, 3 removal marker(s)
• tools/observability/configuration — modified, +96/-173 lines, 39 removal marker(s)
• tools/observability/customization — modified, +240/-247 lines, 65 removal marker(s)
• tools/observability/getting-started — modified, +109/-53 lines, 28 removal marker(s)
• tools/observability/integrations — modified, +76/-13 lines, 10 removal marker(s)
• tools/observability/integrations/datadog — modified, +111/-94 lines, 41 removal marker(s)
• tools/observability/integrations/grafana — modified, +48/-63 lines, 18 removal marker(s)
• tools/observability/integrations/jaeger-prometheus — modified, +76/-56 lines, 25 removal marker(s)
• tools/observability/integrations/newrelic — modified, +52/-52 lines, 16 removal marker(s)
• tools/observability/integrations/prometheus — added, +94/-0 lines
• tools/observability/migrating-to-v5 — added, +340/-0 lines
• tools/observability/reference — modified, +164/-483 lines, 83 removal marker(s)

Other changed files

• articles/tools/observability/integrations/_run-app.adoc (deleted)

Built from 22737ea

[jouni]

Is there a need to keep the v4 documentation for Vaadin 25.2 docs? Could users simply access them in the Vaadin 24 docs?

[caalador]

Not really. It's there more for quick reference while working on the updated docs.