[docs-scanner] Missing detailed documentation page for cacheonly exporter

[docker-agent]

File: content/manuals/build/exporters/_index.md

Issue

The overview page lists seven exporters including cacheonly:

Buildx supports the following exporters:

• image: exports the build result to a container image.
• registry: exports the build result into a container image, and pushes it to the specified registry.
• local: exports the build root filesystem into a local directory.
• tar: packs the build root filesystem into a local tarball.
• oci: exports the build result to the local filesystem in the OCI image layout format.
• docker: exports the build result to the local filesystem in the Docker Image Specification v1.2.0 format.
• cacheonly: doesn't export a build output, but runs the build and creates a cache.

The page also includes a "Cache-only export" use case section describing this exporter.

However, the "What's next" section at the end only links to three pages:

• Image and registry exporters
• OCI and Docker exporters.
• Local and tar exporters

There is no detailed documentation page for the cacheonly exporter.

Why this matters

Readers who want to learn more about the cacheonly exporter will naturally look for a detailed page like the other exporters have. The overview mentions it has specific behavior (creates cache, shows warning messages, is the default in certain conditions), but there's no dedicated page to reference for complete parameter documentation or advanced usage.

This creates an inconsistent documentation structure where six exporters have detailed pages but one does not.

Suggested fix

Either:

1. Create a dedicated page for the cacheonly exporter with its parameters and usage details, or
2. If the cacheonly exporter is simple enough that it doesn't warrant a separate page, add a note in the "What's next" section explaining that the overview contains all available documentation for cacheonly.

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Found by nightly documentation quality scanner