Enable rust formatting preupload hooks

The rustfmt configuration is linked to the default from
build/soong/scripts.

Bug: 157146658
Test: tried uploading badly and correctly formatted rust
Change-Id: Ie104cca1c9f309e4b46acdfabd8c2e17c35180ad
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
new file mode 100644
index 0000000..75ed57c
--- /dev/null
+++ b/PREUPLOAD.cfg
@@ -0,0 +1,5 @@
+[Builtin Hooks]
+rustfmt = true
+
+[Builtin Hooks Options]
+rustfmt = --config-path=rustfmt.toml