[Release] Update release note location (#151931)

**TLDR:** Move the changelog, currently called ["hotfixes to the stable
channel"](https://github.com/flutter/flutter/blob/master/docs/releases/Hotfixes-to-the-Stable-Channel.md),
to the root directory of Flutter/Flutter and rename it to CHANGELOG.md
before the Q3 release cutoff.

This PR accomplishes the following:
1. Renames 'Hotfixes-to-the-stable-channel' to CHANGELOG.md
2. Moves CHANGELOG.md to Flutter/Flutter root.
3. Update references to 'Hotfixes-to-the-stable-channel' to
CHANGELOG.md.

---

#### Background
Flutter has historically kept documentation on wiki pages in the Flutter
repository. Recently, we executed a large-scale migration of our wiki
into a `docs` folder within flutter/flutter.

#### Proposal
I propose relocating the current changelog, which is called ["hotfixes
to the stable
channel"](https://github.com/flutter/flutter/blob/master/docs/releases/Hotfixes-to-the-Stable-Channel.md),
to the root directory of the Flutter/Flutter repository and renaming it
to CHANGELOG.md. This change aims to improve the visibility,
accessibility, and consistency of our documentation processes.

#### Benefits
1. **Unify Dart and Flutter Processes:** This move aligns Flutter’s
changelog management with Dart's practices. As the release manager for
both Dart and Flutter, this unification will streamline the processes
and ensure consistency across projects.

#### Timeline
I would like this proposal **approved or denied before the Q3 release
cutoff** so it may be available within the stable branch.

---

> [!NOTE] 
> This proposal aims to improve our workflow and documentation
standards. I am open to feedback and further discussion on how we can
best implement this change.

dev/conductor/core/lib/src/globals.dart

@@ -29,7 +29,7 @@ const String flutterReleaseHotline =
     'https://mail.google.com/chat/u/0/#chat/space/AAAA6RKcK2k';
 
 const String hotfixToStableWiki =
-    'https://github.com/flutter/flutter/blob/main/docs/releases/Hotfixes-to-the-Stable-Channel.md';
+    'https://github.com/flutter/flutter/blob/main/CHANGELOG.md';
 
 const String flutterAnnounceGroup =
     'https://groups.google.com/g/flutter-announce';

docs/releases/Flutter-build-release-channels.md

@@ -60,4 +60,4 @@ If you really need a particular patch and it's a fix to the flutter/flutter repo
 
 * [Release process](Release-process.md), which describes the details for how we push builds from channel to channel.
 * [Cherrypick process](Flutter-Cherrypick-Process.md), where we cover how to request an issue for cherrypicking.
-* [Release notes](https://flutter.dev/docs/development/tools/sdk/release-notes), where we document changes to each version of the stable channel.
+* [Release notes](https://docs.flutter.dev/release/release-notes), where we document changes to each version of the stable channel.

docs/wiki_archive/User-documentation-index.md

@@ -4,7 +4,7 @@
 Flutter's user-facing documentation should all be on the Flutter web site and the API documentation site:
 
 - https://docs.flutter.dev/
-  - [Release notes](https://flutter.dev/docs/development/tools/sdk/release-notes)
+  - [Release notes](https://docs.flutter.dev/release/release-notes)
 - https://api.flutter.dev/
 
 Historically, experimental documentation was sometimes first written on this wiki and later moved to the web site. This is
@@ -54,4 +54,4 @@ _Contributors: please consider moving this content to the web site or deleting i
 
 ### Release notes
 <!-- don't add things here; user documentation belongs on the web site not the wiki -->
-- [Hotfixes to the Stable Channel](../releases/Hotfixes-to-the-Stable-Channel.md)
+- [Hotfixes to the Stable Channel](../../CHANGELOG.md)