Declare every module's data; the backup holder measures it (hq ADR 0233)

Backup lines are derived from each module's data section instead of written by hand; the holder
measures declared items, reads the array under them, and deletes a retired item only after a last
restore point; the Go providers say each held consumer's size so an empty replacement is seen.

modules/postgres/cmd/postgres-provider/retire_pg.go

@@ -98,7 +98,7 @@ const SetAsideStatement = `SELECT datname, pg_database_size(datname) FROM pg_dat
 
 // Inventory is what this server holds that the mesh made.
 func (c *Client) Inventory(ctx context.Context) (Inventory, error) {
-	inv := Inventory{Active: []string{}, Retired: []Retired{}}
+	inv := Inventory{Active: []string{}, Retired: []Retired{}, Sizes: map[string]int64{}}
 	r, err := c.Query(ctx, "", InventoryStatement)
 	if err != nil {
 		return inv, err
@@ -111,6 +111,9 @@ func (c *Client) Inventory(ctx context.Context) (Inventory, error) {
 		}
 		if login && m.Retired == "" {
 			inv.Active = append(inv.Active, name)
+			if s := sizeOf(size); s >= 0 {
+				inv.Sizes[name] = s
+			}
 			continue
 		}
 		at, _ := time.Parse(time.RFC3339, m.Retired)