termstatus: add stdin and inject into backup command

internal/ui/terminal.go

@@ -13,6 +13,8 @@ type Terminal interface {
 	SetStatus(lines []string)
 	// CanUpdateStatus returns true if the terminal can update the status lines.
 	CanUpdateStatus() bool
+	InputRaw() io.ReadCloser
+	InputIsTerminal() bool
 	// OutputRaw returns the output writer. Should only be used if there is no
 	// other option. Must not be used in combination with Print, Error, SetStatus
 	// or any other method that writes to the terminal.