New app mod flow doc (#48543)

* Initial commit

* replace the image of overview

* Update app mod .NET key features

* update assessment part

* update assessment part

* refine and add follow up

* Initial commit

* replace the image of overview

* Update app mod .NET key features

* update assessment part

* update assessment part

* refine and add follow up

* Add migration steps in quickstart

* Add tasks

* resize image

* preview

* update app mod migration doc with feedback

* revert overview.md

* update for date and content

* update links

* add Aws sqs

* Apply suggestions from code review

* editorial pass

* fix image names

* fix images

* fixes

* add alternative way

* add alternative way

* Fix spacing in quickstart title for clarity

* Delete default chat messages section from quickstart

Removed section on default chat messages for .NET extension.

---------

Co-authored-by: Wenhao Zhang <[email protected]>
Co-authored-by: Ningting Pan <[email protected]>
Co-authored-by: ninpan-ms <[email protected]>
Co-authored-by: Huang Xueyuan (Jessie) <[email protected]>
Co-authored-by: Jessie Huang <[email protected]>
Co-authored-by: alexwolfmsft <[email protected]>
Co-authored-by: Alex Wolf <[email protected]>

Author: 6 people

docs/azure/migration/appmod/faq.md

@@ -122,14 +122,17 @@ If Visual Studio fails to automatically upgrade AppCAT when a new version is ava
 
 ## What should I do if I see "Command failed: No .NET SDKs were found" errors?
 
-This error occurs when AppCAT cannot find a compatible .NET SDK, even if you have other .NET SDKs installed. AppCAT requires the .NET 8.0 SDK to run properly.
+This error occurs when AppCAT cannot find a compatible .NET SDK, even if you have other .NET SDKs installed. AppCAT requires the .NET 9.0 SDK to run properly.
 
 To fix this error:
 
-1. Download and install the .NET 8 SDK from <https://dotnet.microsoft.com/download/dotnet/8.0>.
+1. Download and install the .NET 9.0 SDK from <https://dotnet.microsoft.com/download/dotnet/9.0>.
 2. Restart Visual Studio.
 3. Run the assessment again.
 
+> [!NOTE]
+> The GitHub Copilot app modernization for .NET extension can automatically help you install or upgrade to .NET 9. If you have an older version of the extension, update to the latest version for automatic installation assistance for the required .NET 9.0 SDK.
+
 ## Does the tool store my source code?
 
 No. The tool uses GitHub Copilot in the same way you use it to modify code, and doesn't retain code snippets beyond the immediate session. Telemetry metrics are collected and analyzed to track feature usage and effectiveness.