Move adb_keys to product partition

/adb_keys will be moved to /product/etc/security as it's a
product-specific file. To prevent regression, /adb_keys will be a
symlink to the new location.

Bug: 353430323
Test: boot and connect adb with ADB_VENDOR_KEYS
Change-Id: I3dd200a1583be8f99bd5c30ecfed1bdc544ca783