swaybar: add status_edge_padding command

This adds the bar subcommand `status_edge_padding <padding>` to set the
padding used when the status line is on the right edge of the bar.

include/swaybar/config.h

@@ -44,6 +44,7 @@ struct swaybar_config {
 	bool all_outputs;
 	int height;
 	int status_padding;
+	int status_edge_padding;
 	struct {
 		int top;
 		int right;