Add keys for APEX images for eng/userdebug.

These keys will be used to sign and verify APEX modules on
eng/userdebug devices. The keys may still change, but are
added now to unblock apexd development.

The keys were generated as follows:

$ openssl genrsa -out apex_debug_key.pem 4096
$ avbtool extract_public_key --key apex_debug_key.pem --output apex_debug_key

We'll probably need PRODUCT_APEX_KEYS at some point, but we'll wait
with that until we have build support.

Bug: 112684055
Test: /system/etc/security/apex/apex_debug_key found on-device
Change-Id: I5f4b1cb1eb11be6431146aa4297b50205fbc382e
diff --git a/target/product/base_system.mk b/target/product/base_system.mk
index ef0d0c8..21ac54a 100644
--- a/target/product/base_system.mk
+++ b/target/product/base_system.mk
@@ -305,6 +305,7 @@
 # Packages included only for eng or userdebug builds, previously debug tagged
 PRODUCT_PACKAGES_DEBUG := \
     adb_keys \
+    apex_debug_key \
     iotop \
     logpersist.start \
     perfprofd \