backend: remove yarn cache from built docker image

.changeset/beige-queens-crash.md

@@ -0,0 +1,13 @@
+---
+'@backstage/create-app': patch
+---
+
+Optimized the `yarn install` step in the backend `Dockerfile`.
+
+To apply these changes to an existing app, make the following changes to `packages/backend/Dockerfile`:
+
+Replace the `RUN yarn install ...` line with the following:
+
+```bash
+RUN yarn install --frozen-lockfile --production --network-timeout 600000 && rm -rf "$(yarn cache dir)"
+```

packages/backend/Dockerfile

@@ -7,7 +7,7 @@ WORKDIR /usr/src/app
 # and along with yarn.lock and the root package.json, that's enough to run yarn install.
 ADD yarn.lock package.json skeleton.tar ./
 
-RUN yarn install --frozen-lockfile --production
+RUN yarn install --frozen-lockfile --production --network-timeout 600000 && rm -rf "$(yarn cache dir)"
 
 # This will copy the contents of the dist-workspace when running the build-image command.
 # Do not use this Dockerfile outside of that command, as it will copy in the source code instead.

packages/create-app/templates/default-app/packages/backend/Dockerfile

@@ -7,7 +7,7 @@ WORKDIR /usr/src/app
 # and along with yarn.lock and the root package.json, that's enough to run yarn install.
 ADD yarn.lock package.json skeleton.tar ./
 
-RUN yarn install --frozen-lockfile --production
+RUN yarn install --frozen-lockfile --production --network-timeout 600000 && rm -rf "$(yarn cache dir)"
 
 # This will copy the contents of the dist-workspace when running the build-image command.
 # Do not use this Dockerfile outside of that command, as it will copy in the source code instead.