Address PR comments:

- scripts -> foreman
- drop runHydra
- drop devShell
- move postgresql to buildInputs

foreman/start-hydra.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+# wait for postgresql to listen
+while ! pg_isready -h $(pwd)/.hydra-data/postgres -p 64444; do sleep 1; done
+
+createdb -h $(pwd)/.hydra-data/postgres -p 64444 hydra
+
+hydra-init
+hydra-create-user alice --password foobar --role admin
+
+touch .hydra-data/hydra.conf
+HYDRA_CONFIG=$(pwd)/.hydra-data/hydra.conf exec hydra-dev-server --port 63333