Add apksigner to otatools.zip

BUG: 157735036
Test: Local build.
Change-Id: I95c7001ad520d6b4a415d21ffdef55152b0e82b2
diff --git a/core/Makefile b/core/Makefile
index bd0e00f..7fbf490 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -3594,6 +3594,7 @@
   aapt2 \
   add_img_to_target_files \
   aftltool \
+  apksigner \
   append2simg \
   avbtool \
   blk_alloc_to_base_fs \