JSON Schema for build trace entry

Note, starting to make progress on #11895 by calling it this in the
manual.

src/json-schema-checks/meson.build

@@ -54,6 +54,15 @@ schemas = [
       'single_built_built.json',
     ],
   },
+  {
+    'stem' : 'build-trace-entry',
+    'schema' : schema_dir / 'build-trace-entry-v1.yaml',
+    'files' : [
+      'simple.json',
+      'with-dependent-realisations.json',
+      'with-signature.json',
+    ],
+  },
 ]
 
 # Derivation and Derivation output