docs: add changelog and readme updates for env variable support

Co-authored-by: garrytrinder <11563347+garrytrinder@users.noreply.github.com>

Author: Copilot

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added:
 
+- Setting: Added `env` setting to pass environment variables when starting Dev Proxy
+- Task provider: Added `env` property to task definition for passing environment variables
 - Quick Fixes: Enable local language model fix now adds or updates `languageModel.enabled: true` for supported plugins only
 
 ### Fixed: