Remove invalid page-level applies_to.product from EDOT Cloud Forwarder for GCP docs

[Copilot]

This updates the GCP EDOT Cloud Forwarder page to align its page-level applies_to frontmatter with the documented cumulative-docs schema. The page was mixing deployment and product dimensions, and it used an unrecognized product key (edot_cf_gcp).

• Frontmatter cleanup

  • Removed the page-level product stanza from docs/reference/edot-cloud-forwarder/gcp/index.md
  • Kept the existing serverless and deployment applicability unchanged

• Schema alignment

  • Eliminates the unsupported edot_cf_gcp key
  • Leaves the page with a single primary page-level applicability dimension pattern consistent with the docs guidance

applies_to:
  serverless:
    observability: preview
  deployment:
    ech: preview
    self: unavailable