build: setup docker-compose.dev.yml dev iteration

This is based off of the 5-commit branch at
https://github.com/neobooru/szurubooru/blob/docker-development-setup.

Compared to said branch, we
* Exclude extraneous changes such as
    * Any formatting
    * The use of deprecated/ineffectual top-level `version:` in composer files
* Support controlling $THREADS (modernizing the branch to upstream)
* Integrate into master more cleanly

However, client/docker-start-dev uses a temporary hack -- due to
volume mounting overwriting node_modules at arbitrary points during the
`docker compose build` step, we run `npm i` before any given
`npm run watch`.

To see the effects of this commit in action, run:

    docker compose -f ./docker-compose.dev.yml up

client/Dockerfile

@@ -1,3 +1,26 @@
+FROM --platform=$BUILDPLATFORM node:lts-alpine as development
+WORKDIR /opt/app
+
+RUN apk --no-cache add \
+    dumb-init \
+    nginx \
+    git
+
+RUN ln -sf /opt/app/nginx.conf.docker /etc/nginx/nginx.conf
+RUN rm -rf /var/www
+RUN ln -sf /opt/app/public/ /var/www
+
+COPY package.json package-lock.json ./
+RUN npm install
+
+ARG BUILD_INFO="docker-development"
+ENV BUILD_INFO=${BUILD_INFO}
+ENV BACKEND_HOST="server"
+
+CMD ["/opt/app/docker-start-dev.sh"]
+VOLUME ["/data"]
+
+
 FROM --platform=$BUILDPLATFORM node:lts as builder
 WORKDIR /opt/app