docker: Add Dockerfile for running chasquid+dovecot+letsencrypt

This patch adds a new docker directory, which contains a Dockerfile plus
some additional configuration for creating a container that runs
chasquid+dovecot+letsencrypt.

It also updates the gitlab CI pipeline to automatically build and
publish an image on each commit.

This is experimental and likely to break.

docker/add-user.sh

@@ -0,0 +1,43 @@
+#!/bin/bash
+#
+# Creates a user. If it exists, updates the password.
+#
+# Note this is not robust, it's only for convenience on extremely simple
+# setups.
+
+set -e
+
+read -p "Email (full user@domain format): " EMAIL
+
+if ! echo "${EMAIL}" | grep -q @; then
+	echo "Error: email should have '@'."
+	exit 1
+fi
+
+
+read -p "Password: " -s PASSWORD
+echo
+
+DOMAIN=$(echo echo "${EMAIL}" | cut -d '@' -f 2)
+
+
+# If the domain doesn't exist in chasquid's config, create it.
+mkdir -p "/data/chasquid/domains/${DOMAIN}/"
+
+
+# Encrypt password.
+ENCPASS=$(doveadm pw -u "${EMAIL}" -p "${PASSWORD}")
+
+# Edit dovecot users: remove user if it exits.
+mkdir -p /data/dovecot
+if grep -q "^${EMAIL}:" /data/dovecot/users; then
+	cp /data/dovecot/users /data/dovecot/users.old
+	cat /data/dovecot/users.old | grep -v "^${EMAIL}:" \
+		> /data/dovecot/users
+fi
+
+# Edit dovecot users: add user.
+echo "${EMAIL}:${ENCPASS}::::" >> /data/dovecot/users
+
+echo "${EMAIL} added to /data/dovecot/users"
+