Uffizzi Integration

- add new github actions workflow to create new backstage app, build it
  and create a new preview using uffizzi. uffizzi-build.yml builds
  the image from the PR. Once it completes, uffizzi-preview.yml is
  triggered in the context of the default branch to create the
  preview and post a comment to the Pull request
- add .github/uffizzi folder with the docker-compose template and
  app config for backstage created by uffizzi.

Signed-off-by: Vibhav Bobade <vibhav.bobde@gmail.com>

.github/uffizzi/docker-compose.uffizzi.yml

@@ -0,0 +1,29 @@
+version: '3'
+
+x-uffizzi:
+  ingress:
+    service: backstage
+    port: 7007
+
+services:
+  backstage:
+    image: '${BACKSTAGE_IMAGE}'
+    environment:
+      POSTGRES_HOST: localhost
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: example
+      GITHUB_TOKEN: abc
+      NODE_ENV: production
+    deploy:
+      resources:
+        limits:
+          memory: 500M
+    entrypoint: '/bin/sh'
+    command:
+      - '-c'
+      - "APP_CONFIG_app_baseUrl=$$UFFIZZI_URL APP_CONFIG_backend_baseUrl=$$UFFIZZI_URL APP_CONFIG_auth_environment='production' node packages/backend --config app-config.yaml --config app-config.production.yaml"
+
+  db:
+    image: postgres
+    environment:
+      POSTGRES_PASSWORD: example

.github/uffizzi/uffizzi.production.app-config.yaml

@@ -0,0 +1,10 @@
+app:
+  title: Backstage Uffizzi Environment
+  baseUrl: ${UFFIZZI_URL}
+
+backend:
+  baseUrl: ${UFFIZZI_URL}
+  cors:
+    origin: ${UFFIZZI_URL}
+    methods: [GET, POST, PUT, DELETE]
+    credentials: true