Add Vale docs linting support (#756)

Author: theletterf

.github/workflows/docs-build.yml

@@ -11,6 +11,7 @@ jobs:
   docs-preview:
     uses: elastic/docs-builder/.github/workflows/preview-build.yml@main
     with:
+      enable-vale-linting: true
       path-pattern: docs/**
     permissions:
       deployments: write