docs: preserve /build/metadata/attestations/ aliases on flattened pages

Add backward-compat aliases so links to the pre-flatten URLs
/build/metadata/attestations/sbom/ and
/build/metadata/attestations/slsa-provenance/ continue to resolve.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: dvdksn

content/manuals/build/metadata/provenance.md

@@ -5,6 +5,7 @@ description: >
   Provenance build attestations describe how and where your image was built.
 aliases:
   - /build/attestations/slsa-provenance/
+  - /build/metadata/attestations/slsa-provenance/
 ---
 
 The provenance attestations include facts about the build process, including

content/manuals/build/metadata/sbom.md

@@ -5,6 +5,7 @@ description: |
   SBOM attestations describe what software artifacts an image contains and the artifacts used to create the image.
 aliases:
   - /build/attestations/sbom/
+  - /build/metadata/attestations/sbom/
 ---
 
 SBOM attestations help ensure [software supply chain transparency](/guides/docker-scout/s3c.md) by verifying the software artifacts an image contains and the artifacts used to create the image. Metadata included in an [SBOM](/guides/docker-scout/sbom.md) for describing software artifacts may include: