Added yarn archive to produce a build tarball

fixes https://github.com/TryGhost/Ghost/issues/16835

- this reimplements a command to product a tarball with Ghost after we
  took over `yarn build` for package-specific build steps

ghost/core/package.json

@@ -20,6 +20,7 @@
   "contributors": "https://github.com/TryGhost/Ghost/graphs/contributors",
   "license": "MIT",
   "scripts": {
+    "archive": "npm pack",
     "start": "node index",
     "setup": "knex-migrator init",
     "build": "yarn build:css",

package.json

@@ -20,6 +20,7 @@
     "**/node_modules/**"
   ],
   "scripts": {
+    "archive": "yarn workspace ghost run archive",
     "build": "lerna run build",
     "dev:debug": "DEBUG_COLORS=true DEBUG=@tryghost*,ghost:* yarn dev",
     "dev:admin": "node .github/dev.js --admin",