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

PREUPLOAD.cfg

+[Builtin Hooks]
+rustfmt = true
+
+[Builtin Hooks Options]
+rustfmt = --config-path=rustfmt.toml

rustfmt.toml

+../../../build/soong/scripts/rustfmt.toml
\ No newline at end of file