Update CHANGELOG.md

Author: Dani-Kirby

CHANGELOG.md

@@ -1,3 +1,10 @@
+## 2.1.0
+- New Feature:
+  - Environment-Based Client Initialization
+- Bug Fixes:
+  - Fix missing `OTHERS` value in `Shipment Carrier` enum model
+  - Update Transaction Search API naming in docs
+
 ## 2.0.0
 - Breaking Changes:
   - Several model renames for more precise mapping to controllers
@@ -17,4 +24,4 @@
 - Documentation updates
 
 ## 1.0.0
-- GA Release for Orders, Payments, and Vault APIs
+- GA Release for Orders, Payments, and Vault APIs