Update dates, and add upcoming 3.x

Author: farleyb-amazon

SUPPORT_POLICY.rst

@@ -28,6 +28,10 @@ This table describes the current support status of each major version of the AWS
     * - 2.x
       - General Availability 
       - Maintenance
-      - 2021-06-30
+      - 2021-07-01
+    * - 3.x
+      - 
+      - General Availability 
+      - 2021-07-01
 
 .. _AWS SDKs and Tools Maintenance Policy: https://docs.aws.amazon.com/sdkref/latest/guide/maint-policy.html#version-life-cycle