feat(agentic chat): Add changelog (aws#7211)

Add changelog for the agentic chat release



---

- Treat all work as PUBLIC. Private `feature/x` branches will not be
squash-merged at release time.
- Your code changes must meet the guidelines in
[CONTRIBUTING.md](https://github.com/aws/aws-toolkit-vscode/blob/master/CONTRIBUTING.md#guidelines).
- License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

Author: opieter-aws

packages/amazonq/.changes/next-release/Feature-ef539952-41de-40d0-870e-94aee31f36d3.json

@@ -0,0 +1,4 @@
+{
+	"type": "Feature",
+	"description": "Agentic coding experience: Amazon Q can now write code and run shell commands on your behalf"
+}