microdroid_manager: initial impl

It is started by init in microdroid and executes a command specified in
a VM payload config.

Bug: 189301496
Test: MicrodroidHostTestCases
  (in a microdroid, run /system/bin/microdroid_manager manulally)
Change-Id: I85c7e370d4a0dcf58b4aafbe6e9fba73e69c2a44
diff --git a/microdroid/signature/Android.bp b/microdroid/signature/Android.bp
index 35c4e9e..1ce7805 100644
--- a/microdroid/signature/Android.bp
+++ b/microdroid/signature/Android.bp
@@ -38,6 +38,14 @@
     ],
 }
 
+rust_protobuf {
+    name: "libmicrodroid_signature_proto_rust",
+    crate_name: "microdroid_signature",
+    protos: ["microdroid_signature.proto"],
+    source_stem: "microdroid_signature",
+    host_supported: true,
+}
+
 cc_binary {
     name: "mk_payload",
     srcs: [