Create changelog for v1.20.1 release (#5942)

* Initial plan

* Complete v1.20.1 changelog

Co-authored-by: rajeshkamal5050 <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: rajeshkamal5050 <[email protected]>

Author: Copilot

cli/azd/CHANGELOG.md

@@ -1,13 +1,19 @@
 # Release History
 
-## 1.21.0-beta.1 (Unreleased)
+## 1.20.1 (2025-10-17)
 
 ### Features Added
 
-### Breaking Changes
+- [[#5693]](https://github.com/Azure/azure-dev/pull/5693) Add GitHub Copilot LLM backend integration for AI-assisted development workflows.
+- [[#5847]](https://github.com/Azure/azure-dev/pull/5847) Add support for language frameworks from extensions.
+- [[#5881]](https://github.com/Azure/azure-dev/pull/5881) Display Aspire dashboard URL for App Service deployments.
+- [[#5841]](https://github.com/Azure/azure-dev/pull/5841) Add `prepublish` and `postpublish` hooks to v1.0 azure.yaml schema.
 
 ### Bugs Fixed
 
+- [[#5939]](https://github.com/Azure/azure-dev/pull/5939) Fix Container App resource existence check returning incorrect results.
+- [[#5930]](https://github.com/Azure/azure-dev/pull/5930) Improve diagnostic message clarity for missing --environment flag.
+
 ### Other Changes
 
 ## 1.20.0 (2025-10-08)

cli/version.txt

@@ -1 +1 @@
-1.21.0-beta.1
+1.20.1