PREUPLOAD: Enforce jsonlint in preupload

Checks syntax and simple brace balances for all JSON files.

Test: Edit any json file and try upload
Bug: 127794899
Change-Id: Iae810239db56de48c73a4ff3f5fcebc7f805203b
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
new file mode 100644
index 0000000..37ebb5e
--- /dev/null
+++ b/PREUPLOAD.cfg
@@ -0,0 +1,2 @@
+[Builtin Hooks]
+jsonlint = true