Add cos/tools to COS source tree

BUG=b/465210631
TEST=repo init & sync
RELEASE_NOTE=None

Change-Id: Id6176d13ab1114cd9988ce9a31fb7c3428bbd3aa
Reviewed-on: https://cos-review.googlesource.com/c/cos/manifest/+/138846
Tested-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: Miri Amarilio <mirilio@google.com>
Reviewed-by: Kevin Berry <kpberry@google.com>

external_full.xml

diff --git a/external_full.xml b/external_full.xml
index 5982fe8..823e41c 100644
--- a/external_full.xml
+++ b/external_full.xml
@@ -219,6 +219,9 @@
            name="cos/repohooks"
            revision="refs/heads/master" />
 
+  <project path="src/cos_tools"
+           name="cos/tools"
+           revision="refs/heads/master" />
   <project path="src/platform/cobble"
            name="cos/cobble" />
   <project path="manifest" name="cos/manifest" >