Add preupload hooks to build/blueprint

Run gofmt and bpfmt during preupload, and warn about uses of
DO NOT MERGE.

Test: repo upload
Change-Id: I5f8a318f9ec1dbca897d25f25107df36d160e1f6
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
new file mode 100644
index 0000000..317f5c4
--- /dev/null
+++ b/PREUPLOAD.cfg
@@ -0,0 +1,6 @@
+[Builtin Hooks]
+gofmt = true
+bpfmt = true
+
+[Hook Scripts]
+do_not_use_DO_NOT_MERGE = ${REPO_ROOT}/build/soong/scripts/check_do_not_merge.sh ${PREUPLOAD_COMMIT}