docs(schema): the schemas and the command help for the scrolling layout

schema.json gets center_focused_column as a boolean or one of Never, Always
and OnOverflow, the options of the module follow it, and docs/cli has the
new commands.

docs/cli/toggle-column-stack.md

@@ -0,0 +1,11 @@
+```text
+Stack the windows of the focused column of the Scrolling layout, or spread the focused stack out
+into a column with a window in each slot
+
+Usage: toggle-column-stack
+
+Options:
+  -h, --help
+          Print help
+
+```