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/db/src/migrations/0036_cheerful_nitro.sql

@@ -0,0 +1,9 @@
+CREATE TABLE "instance_settings" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"singleton_key" text DEFAULT 'default' NOT NULL,
+	"experimental" jsonb DEFAULT '{}'::jsonb NOT NULL,
+	"created_at" timestamp with time zone DEFAULT now() NOT NULL,
+	"updated_at" timestamp with time zone DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+CREATE UNIQUE INDEX "instance_settings_singleton_key_idx" ON "instance_settings" USING btree ("singleton_key");