Ditch dbmate in favour of internal migration

such that migration files can be embedded

docker/rootfs/etc/cont-init.d/30-dbmate

@@ -1,16 +0,0 @@
-#!/usr/bin/with-contenv bash
-
-CYAN='\E[1;36m'
-YELLOW='\E[1;33m'
-MAGENTA='\E[1;35m'
-RESET='\E[0m'
-
-if [ "$LOG_LEVEL" == "debug" ]; then
-	echo -e "${MAGENTA}[DEBUG] ${CYAN}DATABASE_URL=${YELLOW}${DATABASE_URL}${RESET}"
-fi
-
-# Firstly create the sqlite database if it doesn't already exist
-# and run any migrations required
-echo -e "${YELLOW}Running dbmate migrations ...${RESET}"
-s6-setuidgid npmuser /bin/dbmate up || exit 1
-echo -e "${GREEN}Completed dbmate migrations!${RESET}"