updating dockerfile and creating task to build the image from the host

Dockerfile

@@ -1,22 +1,6 @@
-FROM node:12 as builder
-WORKDIR /app
-
-COPY package.json yarn.lock .yarnrc .npmrc /app/
-COPY .yarn /app/.yarn
-COPY packages /app/packages
-COPY plugins /app/plugins
-
-RUN yarn
-
-COPY lerna.json tsconfig.json .eslintignore .eslintrc.js /app/
-COPY scripts/ /app/scripts
-
-RUN yarn build
-
 FROM nginx:mainline
 
-COPY --from=builder /app/packages/app/build /usr/share/nginx/html
-
+COPY packages/app/build /usr/share/nginx/html
 COPY docker/default.conf.template /etc/nginx/conf.d/default.conf.template
 COPY docker/run.sh /usr/local/bin/run.sh
 CMD run.sh

package.json

@@ -9,6 +9,7 @@
     "bundle": "yarn build && yarn workspace example-app bundle",
     "build": "lerna run build",
     "test": "cross-env CI=true lerna run test --since origin/master -- --coverage",
+    "docker-build": "yarn build && docker build . -t spotify/backstage",
     "create-plugin": "backstage-cli create-plugin",
     "release": "if [ \"$(git symbolic-ref --short HEAD)\" = master ]; then echo \"don't try to release master\"; exit 1; else lerna version --no-push; fi",
     "lint": "cross-env CI=true lerna run lint --since origin/master --",