Update Dockerfile.nginx (#269)

### Description
webapp/Dockerfile.nginx flag needs to have --production=false otherwise
react-scripts won't be installed to build the webapp

### Contribution Checklist

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- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [Contribution
Guidelines](https://github.com/microsoft/copilot-chat/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
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raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

docker/webapp/Dockerfile.nginx

@@ -22,7 +22,7 @@ RUN yarn install \
   --prefer-offline \
   --frozen-lockfile \
   --non-interactive \
-  --production=true
+  --production=false
 
 RUN yarn build
 
@@ -31,4 +31,4 @@ FROM nginx:stable-alpine
 EXPOSE 3000
 RUN sed -i 's/80/3000/g' /etc/nginx/conf.d/default.conf
 COPY --from=builder /app/build /usr/share/nginx/html
-CMD ["nginx", "-g", "daemon off;"]
+CMD ["nginx", "-g", "daemon off;"]