json schema: set schema version to draft-4, clarify taplo support

cli/src/config-schema.json

@@ -1,5 +1,6 @@
 {
-    "$schema": "http://json-schema.org/draft-07/schema",
+    "$schema": "http://json-schema.org/draft-04/schema",
+    "$comment": "`taplo` and the corresponding VS Code plugins only support draft-04 verstion of JSON Schema, see <https://taplo.tamasfe.dev/configuration/developing-schemas.html>. draft-07 is mostly compatible with it, newer versions may not be.",
     "title": "Jujutsu config",
     "type": "object",
     "description": "User configuration for Jujutsu VCS. See https://jj-vcs.github.io/jj/latest/config/ for details",