build(docker): reorder instructions for build caching

Dockerfile

@@ -3,25 +3,30 @@ FROM node:lts-bullseye-slim
 # Workdir
 WORKDIR /usr/app
 
-# Copy and install packages
-COPY . .
+# Create temp folder for files to be stored whilst being converted
+RUN mkdir -p ./src/temp/ && \
+    ## Allow for temp folder to be manipulated
+    chown -R node ./src/
+
+# Install OS dependencies
 # Curl needed for healthcheck command
-RUN apt-get -q update && \
+RUN apt-get -q update &&\
     apt-get -y --no-install-recommends install curl poppler-data poppler-utils unrtf && \
     apt-get clean && \
-    rm -rf /var/lib/apt/lists/* && \
-    npm ci --ignore-scripts --omit=dev && \
+    rm -rf /var/lib/apt/lists/*
+
+# Copy and install node dependencies
+COPY package.json package-lock.json ./
+RUN npm ci --ignore-scripts --omit=dev && \
     npm cache clean --force && \
     chown node ./node_modules/htmltidy2/bin/linux64/tidy && \
     chmod 100 ./node_modules/htmltidy2/bin/linux64/tidy && \
     # Remove included Windows binaries
     rm -rf ./node_modules/node-poppler/src/lib/* && \
     rm -rf ./node_modules/node-unrtf/src/lib/*
 
-# Create temp folder for files to be stored whilst being converted
-RUN mkdir ./src/temp/ && \
-    ## Allow for temp folder to be manipulated
-    chown -R node ./src/
+# Copy source
+COPY . .
 
 # Node images provide 'node' unprivileged user to run apps and prevent
 # privilege escalation attacks