Add postgres data volumes to state

imageroot/etc/state-include.conf

@@ -3,6 +3,7 @@
 # Syntax reference: https://pkg.go.dev/path/filepath#Glob
 # Restic --files-from: https://restic.readthedocs.io/en/stable/040_backup.html#including-files
 # List here what you want to save during backup : volumes or file Path
+volume/postgres-data
 state/joplin.pg_dump
 state/database.env
 state/app.env