Add bazel staging mode to soong build.

This is to use bazel to build targets that are being prepared for an
incipient release to the prod mode allowlist.

Bug: 254265047
Test: m nothing
Test: m nothing --bazel-mode-dev
Test: m nothing --bazel-mode-staging
Change-Id: Ic78a59cf51dba83ef1ac26483586560ea9b24aaf
diff --git a/android/config.go b/android/config.go
index 4992882..1ed405b 100644
--- a/android/config.go
+++ b/android/config.go
@@ -97,6 +97,11 @@
 	// allowlisted on an experimental basis.
 	BazelDevMode
 
+	// Use bazel during analysis of a few allowlisted build modules. The allowlist
+	// is considered "staging, as these are modules being prepared to be released
+	// into prod mode shortly after.
+	BazelStagingMode
+
 	// Use bazel during analysis of build modules from an allowlist carefully
 	// curated by the build team to be proven stable.
 	BazelProdMode