all: release v0.6.0

This commit will be tagged v0.6.0.

Change-Id: Ie411e90bc6d767a87ffe868bd2df47972f695442
Reviewed-on: https://code-review.googlesource.com/c/google-api-go-client/+/41711
Reviewed-by: Tyler Bui-Palsulich <tbp@google.com>
Reviewed-by: Chris Broadfoot <cbro@google.com>
Reviewed-by: kokoro <noreply+kokoro@google.com>

CHANGES.md

@@ -1,3 +1,11 @@
+# v0.6.0
+
+- Add support for GCP DirectPath.
+- Various updates to autogenerated clients.
+
+_Please note:_ the release version is not indicative of an individual client's
+stability or version.
+
 # v0.5.0
 
 - Better support for google.api.HttpBody.