🐋 fix(Dockerfile): Optimize client build by caching npm install step

Dockerfile.multi

@@ -13,11 +13,12 @@ RUN npm run build
 # React client build
 FROM data-provider-build AS client-build
 WORKDIR /app/client
+COPY ./client/package*.json ./
+RUN npm install
 COPY ./client/ ./
 # Copy data-provider to client's node_modules
 RUN mkdir -p /app/client/node_modules/librechat-data-provider/
 RUN cp -R /app/packages/data-provider/* /app/client/node_modules/librechat-data-provider/
-RUN npm install
 ENV NODE_OPTIONS="--max-old-space-size=2048"
 RUN npm run build