New product config flag to gate blueprint modules

Example usage:
PRODUCT_INCLUDE_TAGS += use_myspecial_sdk

This also populates the allowlist with go/nogo mainline tags. Usage of
`PRODUCT_INCLUDE_TAGS` outside this allowlist will raise an error
in product config

Test: TH

Change-Id: Ica82a8f65cbfda600d72fc54fb873c1eaa1666a7
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 7d3ae23..a89db4f 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -300,6 +300,8 @@
 
 $(call add_json_bool, IgnorePrefer32OnDevice, $(filter true,$(IGNORE_PREFER32_ON_DEVICE)))
 
+$(call add_json_list, IncludeTags,                $(PRODUCT_INCLUDE_TAGS))
+
 $(call json_end)
 
 $(file >$(SOONG_VARIABLES).tmp,$(json_contents))