docs: document release process

docs/dev/how-to-release.md

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+# How to release
+
+## Staging environment
+
+This is automatically done by the CI of github,
+see `.github/workflows/container-build.yml`.
+
+The deployment uses docker compose with specific environments variables
+and the `docker/prod.yml` overlay.
+
+As soon as you merge a pull request in the `main` branch,
+the action is triggered. You can see it at
+https://github.com/openfoodfacts/openfoodfacts-server/actions/workflows/container-build.yml
+
+## Production environment
+
+Product Opener is deployed on a container in Proxmox.
+The container is a debian server, it must follow the `backend` container version.
+
+In the command lines, I use $SERVICE and $VERSION variables,
+corresponding to the service short name (off, opf, etc.) and the version tag.
+
+To deploy you need to execute the following steps:
+1. merge the Release Please pull request.
+   This will create a new release / version tag on github
+1. update the code:
+   ```bash
+   sudo -u off bash
+   cd /srv/$SERVICE
+   git fetch
+   git checkout $VERSION
+   ```
+1. update the frontend assets you just downloaded
+   ```bash
+   sudo -u off /srv/$SERVICE/scripts/deploy/install-dist-files.sh
+   ```
+1. restart services
+   ```bash
+   sudo systemctl daemon-reload
+   sudo systemctl restart nginx apache2
+   sudo systemctl restart cloud_vision_ocr@$SERVICE.service
+   ```

scripts/deploy/install-dist-files.sh

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+#!/usr/bin/env bash
+
+# this script is a helper for deployment
+# it downloads the assets for a version and extracts them
+# It must be followed by install-dist-files.sh which will install files
+
+
+# fail on error
+set -e
+
+if [[ -z "$1" ]]
+then
+  echo "Usage: $0 <version> [<instance short name>]"
+  echo "ex: $0 v2.53.0 off"
+  echo "If <instance short name> is not provided, it will be the server name"
+  exit 2
+fi
+
+VERSION=$1
+
+if [[ -n $2 ]]
+then
+  SERVICE=$2
+else
+  SERVICE=$(hostname)
+fi
+
+if [[ $(whoami) != off ]]
+then
+  echo "This script must be run as the off user"
+  exit 3
+fi
+
+echo "Downloading dist files $VERSION for $SERVICE"
+# get archive and untar
+curl --fail --location https://github.com/openfoodfacts/openfoodfacts-server/releases/download/$VERSION/frontend-dist.tgz -o /tmp/frontend-dist.tgz
+rm -rf /srv/$SERVICE-dist/tmp/$VERSION || true
+mkdir -p /srv/$SERVICE-dist/tmp/$VERSION
+tar --directory=/srv/$SERVICE-dist/tmp/$VERSION -xzf /tmp/frontend-dist.tgz
+# remove old files
+rm -rf /srv/$SERVICE-dist/tmp/old || true
+mkdir /srv/$SERVICE-dist/tmp/old
+# swap current version and old version
+shopt -s extglob  # extended globbing
+mv /srv/$SERVICE-dist/!(tmp) /srv/$SERVICE-dist/tmp/old
+mv /srv/$SERVICE-dist/tmp/$VERSION/* /srv/$SERVICE-dist/
+rmdir /srv/$SERVICE-dist/tmp/$VERSION