Include .npmrc in Docker build step to ensure @owlboard/ts-types can be installed as a dev dependency for tsc

Signed-off-by: Fred Boniface <fred@fjla.uk>

Dockerfile

@@ -1,7 +1,8 @@
 FROM node:20 as builder
 WORKDIR /usr/src/app
 COPY ./package*.json ./
-RUN npm i
+COPY ./.npmrc ./
+RUN npm install
 COPY . .
 # Ideally the tests should be run separately in a CI/CD workflow rather than during the build
 RUN npm run test