changelog: add entry for v3 task metadata endpoint
# Changelog
-## 1.20.4-dev
+## 1.21.0-dev
+* Feature - Add v3 task metadata support for awsvpc, host and bridge network mode
+
+## 1.20.4
* Bug - Fixed a bug where Windows drive volume couldn't be mounted [#1571](https://github.com/aws/amazon-ecs-agent/pull/1571)
* Bug - Fixed a bug where the Agent's Windows binaries didn't use consistent naming [#1573](https://github.com/aws/amazon-ecs-agent/pull/1573)
* Bug - Fixed a bug where a port used by WinRM service was not reserved by the Agent by default [#1577](https://github.com/aws/amazon-ecs-agent/pull/1577)
