[editoral] Inline Hugo front matter

[thompson-tomo]

Inlining will allow us to simplify the importing and processing of doc pages into OTel.io.

• In support of: [CI] Render spec pages without preprocessing opentelemetry.io#6101
• This is the opamp equivalent of: [editorial] Inline Hugo front matter opentelemetry-specification#4029

/cc @open-telemetry/docs-maintainers