feat: add defaultDateType config

quartz/plugins/emitters/contentIndex.ts

@@ -1,4 +1,5 @@
 import { GlobalConfiguration } from "../../cfg"
+import { getDate } from "../../components/Date"
 import { FilePath, FullSlug, SimpleSlug, simplifySlug } from "../../util/path"
 import { QuartzEmitterPlugin } from "../types"
 import path from "path"
@@ -74,7 +75,7 @@ export const ContentIndex: QuartzEmitterPlugin<Partial<Options>> = (opts) => {
       const linkIndex: ContentIndex = new Map()
       for (const [_tree, file] of content) {
         const slug = file.data.slug!
-        const date = file.data.dates?.modified ?? new Date()
+        const date = getDate(ctx.cfg.configuration, file.data) ?? new Date()
         if (opts?.includeEmptyFiles || (file.data.text && file.data.text !== "")) {
           linkIndex.set(slug, {
             title: file.data.frontmatter?.title!,