chore: fix dockerfile with pnpm

Author: larsrickert

.dockerignore

@@ -1,5 +1,7 @@
+.git
 node_modules
 .vscode
 .idea
 dist
 /cli
+docs/.vitepress/cache

Dockerfile

@@ -1,12 +1,16 @@
 # build stage
-FROM node:17 as build
+FROM node:18 as build
 
 WORKDIR /app
-COPY package*.json ./
-RUN npm ci
+
+# install pnpm as defined in package.json
+COPY pnpm-lock.yaml package.json ./
+RUN npm i -g $(node -p "require('./package.json').packageManager")
+
+RUN pnpm install --frozen-lockfile
 
 COPY . ./
-RUN npm run docs:build
+RUN pnpm docs:build
 
 # production stage
 FROM nginx:stable-alpine