Start signing internal v3 json

Now that the PR on the main brew repo got merged in we're generating
the internal v3 JSON but we're not storing or using it anywhere.
This updates the scheduled generation task to not only store the
resulting JSON but also sign it to allow us to use it as a reference
when building the loader code.

.github/workflows/scheduled.yml

@@ -74,7 +74,7 @@ jobs:
           HOMEBREW_DEVELOPER: 1
 
       - name: Archive data
-        run: tar czvf data-core.tar.gz _data/formula/ _data/formula_canonical.json api/formula/ api/formula_tap_migrations.json formula/
+        run: tar czvf data-core.tar.gz _data/formula/ _data/formula_canonical.json api/formula/ api/formula_tap_migrations.json formula/ api/internal/v3/homebrew-core.json
 
       - uses: actions/upload-artifact@v3
         with:

script/sign-json.rb

@@ -17,6 +17,7 @@
   ROOT/"_site/api/cask.json",
   ROOT/"_site/api/formula_tap_migrations.json",
   ROOT/"_site/api/cask_tap_migrations.json",
+  ROOT/"_site/api/internal/v3/homebrew-core.json",
 ].each do |path|
   data_string = path.read