Add instance experimental setting for isolated workspaces

Introduce a singleton instance_settings store and experimental settings API, add the Experimental instance settings page, and gate execution workspace behavior behind the new enableIsolatedWorkspaces flag.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/shared/src/validators/instance.ts

@@ -0,0 +1,10 @@
+import { z } from "zod";
+
+export const instanceExperimentalSettingsSchema = z.object({
+  enableIsolatedWorkspaces: z.boolean().default(false),
+}).strict();
+
+export const patchInstanceExperimentalSettingsSchema = instanceExperimentalSettingsSchema.partial();
+
+export type InstanceExperimentalSettings = z.infer<typeof instanceExperimentalSettingsSchema>;
+export type PatchInstanceExperimentalSettings = z.infer<typeof patchInstanceExperimentalSettingsSchema>;