Backstage Yarn Plugin Docs adjustments

Signed-off-by: Andre Wanlin <awanlin@spotify.com>

docs/deployment/docker.md

@@ -85,6 +85,7 @@ WORKDIR /app
 # Copy files needed by Yarn
 COPY --chown=node:node .yarn ./.yarn
 COPY --chown=node:node .yarnrc.yml ./
+COPY --chown=node:node backstage.json ./
 
 # This switches many Node.js dependencies to production mode.
 ENV NODE_ENV=production
@@ -181,7 +182,7 @@ the repo root:
 FROM node:20-bookworm-slim AS packages
 
 WORKDIR /app
-COPY package.json yarn.lock ./
+COPY backstage.json package.json yarn.lock ./
 COPY .yarn ./.yarn
 COPY .yarnrc.yml ./
 
@@ -219,6 +220,7 @@ WORKDIR /app
 COPY --from=packages --chown=node:node /app .
 COPY --from=packages --chown=node:node /app/.yarn ./.yarn
 COPY --from=packages --chown=node:node /app/.yarnrc.yml  ./
+COPY --from=packages --chown=node:node /app/backstage.json ./
 
 RUN --mount=type=cache,target=/home/node/.cache/yarn,sharing=locked,uid=1000,gid=1000 \
     yarn install --immutable
@@ -266,7 +268,9 @@ WORKDIR /app
 # Copy the install dependencies from the build stage and context
 COPY --from=build --chown=node:node /app/.yarn ./.yarn
 COPY --from=build --chown=node:node /app/.yarnrc.yml  ./
+COPY --from=build --chown=node:node /app/backstage.json ./
 COPY --from=build --chown=node:node /app/yarn.lock /app/package.json /app/packages/backend/dist/skeleton/ ./
+
 # Note: The skeleton bundle only includes package.json files -- if your app has
 # plugins that define a `bin` export, the bin files need to be copied as well to
 # be linked in node_modules/.bin during yarn install.