WIP: postgres db support

Part of https://git.coopcloud.tech/coop-cloud/matrix-synapse/issues/2.

entrypoint.sh.tmpl

@@ -1,7 +1,29 @@
 #!/bin/bash
 
-if [[ ! -f /data/homeserver.yaml ]]; then
-	/start.py generate
-fi
+set -e
+
+file_env() {
+   local var="$1"
+   local fileVar="${var}_FILE"
+   local def="${2:-}"
+
+   if [ "${!var:-}" ] && [ "${!fileVar:-}" ]; then
+      echo >&2 "error: both $var and $fileVar are set (but are exclusive)"
+      exit 1
+   fi
+
+   local val="$def"
+
+   if [ "${!var:-}" ]; then
+      val="${!var}"
+   elif [ "${!fileVar:-}" ]; then
+      val="$(< "${!fileVar}")"
+   fi
+
+   export "$var"="$val"
+   unset "$fileVar"
+}
+
+file_env "POSTGRES_DB_PASSWORD"
 
 /start.py