Add variables for configuring Soong plugins

See the Soong commit for detailed usage.

Bug: 76168832
Test: define some variables, use them
Change-Id: Ia8af5b6ec1cb3f12cbc1fee582a309eebb340b7c
Merged-In: Ia8af5b6ec1cb3f12cbc1fee582a309eebb340b7c
(cherry picked from commit eaacf5b2851c6a9aac27b4e6a3c7bc8ce320f1ab)
diff --git a/core/config.mk b/core/config.mk
index d9f14fa..43f1564 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -182,6 +182,9 @@
 # Set common values
 # ###############################################################
 
+# Initialize SOONG_CONFIG_NAMESPACES so that it isn't recursive.
+SOONG_CONFIG_NAMESPACES :=
+
 # Set the extensions used for various packages
 COMMON_PACKAGE_SUFFIX := .zip
 COMMON_JAVA_PACKAGE_SUFFIX := .jar