fix: DigitalOcean template (#4287)

## About the changes
Instead of building from source (we require Node 18 but [DigitalOcean
buildpack currently does not support
it](https://www.digitalocean.com/community/questions/app-platform-node-build-pack-can-t-use-node-version-18)),
we're going to use our Docker image from DockerHub:
https://hub.docker.com/r/unleashorg/unleash-server

Additionally, I realized that our Dockerfile only works in our CI (or
performing a pre-build step which consists of building the frontend).
With this PR I've also made a change to build the frontend if needed.
That way our CI will continue to be optimal while anyone trying to build
it from source will be able to do it by just running `docker build .`

Closes #4261

.do/deploy.template.yaml

@@ -2,11 +2,11 @@ spec:
   name: unleash
   services:
     - name: unleash-server
-      git:
-        branch: main
-        repo_clone_url: https://github.com/Unleash/unleash.git
-      build_command: 'yarn build'
-      run_command: 'yarn start'
+      image:
+        registry_type: DOCKER_HUB
+        registry: unleashorg
+        repository: unleash-server
+        tag: latest
       envs:
         - key: DATABASE_URL
           scope: RUN_TIME

Dockerfile

@@ -10,7 +10,9 @@ RUN yarn config set network-timeout 300000
 
 RUN yarn install --frozen-lockfile --ignore-scripts && yarn prepare:backend && yarn local:package
 
-# frontend/build should already exist (it needs to be built in the local filesystem
+# frontend/build should already exist (it needs to be built in the local filesystem but in case of a fresh build we'll build it here)
+RUN yarn build:frontend:if-needed
+
 RUN mkdir -p /unleash/build/frontend && mv /unleash/frontend/build /unleash/build/frontend/build
 
 WORKDIR /unleash/docker

package.json

@@ -34,6 +34,7 @@
     "copy-templates": "copyfiles -u 1 src/mailtemplates/**/*.mustache dist/",
     "build:backend": "tsc --pretty --strictNullChecks false",
     "build:frontend": "yarn --cwd ./frontend run build",
+    "build:frontend:if-needed": "if [ ! -d ./frontend/build ]; then yarn install --cwd ./frontend --frozen-lockfile --ignore-scripts && yarn build:frontend; fi",
     "build": "concurrently \"yarn:copy-templates\" \"yarn:build:frontend\" \"yarn:build:backend\"",
     "dev:backend": "TZ=UTC NODE_ENV=development tsc-watch --strictNullChecks false --onSuccess \"node dist/server-dev.js\"",
     "dev:frontend": "wait-on tcp:4242 && yarn --cwd ./frontend run dev",