feat: support emitters defining external resources, emit link from contentindex directly

quartz/util/resources.tsx

@@ -1,5 +1,6 @@
 import { randomUUID } from "crypto"
 import { JSX } from "preact/jsx-runtime"
+import { QuartzPluginData } from "../plugins/vfile"
 
 export type JSResource = {
   loadTime: "beforeDOMReady" | "afterDOMReady"
@@ -62,4 +63,5 @@ export function CSSResourceToStyleElement(resource: CSSResource, preserve?: bool
 export interface StaticResources {
   css: CSSResource[]
   js: JSResource[]
+  additionalHead: (JSX.Element | ((pageData: QuartzPluginData) => JSX.Element))[]
 }