Add a switch to configure APEX payload type

PRODUCT_DEFAULT_APEX_PAYLOAD_TYPE is a new product variable to set the
default APEX payload type. (ext4 is the default)

OVERRIDE_PRODUCT_DEFAULT_APEX_PAYLOAD_TYPE is to override it from CLI.

Bug: 377388109
Test: OVERRIDE_PRODUCT_DEFAULT_APEX_PAYLOAD_TYPE=erofs m
  # APEXes contain erofs payload images
Change-Id: Icc5908a230abe499a8f1fdb1aba1f959bdc86213
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 0f82b68..d823905 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -274,6 +274,7 @@
 $(call add_json_str,  DeviceCurrentApiLevelForVendorModules,  $(BOARD_CURRENT_API_LEVEL_FOR_VENDOR_MODULES))
 
 $(call add_json_bool, CompressedApex, $(filter true,$(PRODUCT_COMPRESSED_APEX)))
+$(call add_json_str, DefaultApexPayloadType, $(PRODUCT_DEFAULT_APEX_PAYLOAD_TYPE))
 
 $(call add_json_bool, BoardUsesRecoveryAsBoot, $(filter true,$(BOARD_USES_RECOVERY_AS_BOOT)))