Exit ffs startup script if migrations fail (open-telemetry#402)

src/featureflagservice/rel/overlays/bin/server

@@ -1,6 +1,6 @@
 #!/bin/sh
 cd -P -- "$(dirname -- "$0")"
 
-./featureflagservice eval Featureflagservice.Release.migrate
+./featureflagservice eval Featureflagservice.Release.migrate || { echo "Database setup or migrations failed."; exit 1; }
 
 PHX_SERVER=true exec ./featureflagservice start