Create yaml and mdx pages and add first entry for DNS

Author: RebeccaTamachiro

src/content/changelogs/dns.yaml

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+---
+link: "/dns/changelog/"
+productName: DNS
+productLink: "/dns/"
+productArea: Core platform
+productAreaLink: /fundamentals/reference/changelog/performance/
+entries:
+  - publish_date: "2024-10-15"
+    title: Quote validation for TXT records added via dashboard
+    description: |-
+      When creating TXT records via the dashboard users will now find:
+      - Field validation errors if double quotes `"` are added inconsistently.
+      - Automatically quoted TXT content upon save if no quotes exist in the record content field.

src/content/docs/dns/changelog.mdx

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+---
+pcx_content_type: changelog
+title: Changelog
+changelog_file_name:
+  - dns
+sidebar:
+  order: 15
+---
+
+import { ProductChangelog } from "~/components";
+
+{/* <!-- Actual content lives in /src/content/changelogs/dns.yaml. Update the file there for new entries to appear here. For more details, refer to https://developers.cloudflare.com/style-guide/documentation-content-strategy/content-types/changelog/#yaml-file --> */}
+
+<ProductChangelog />