Add last_update_seconds.

Bug: 211458160
Change-Id: I45eed42c0126cfde3b1b632c3ed90af57bdde455
diff --git a/microdroid_manager/src/instance.rs b/microdroid_manager/src/instance.rs
index aadb71f..cb59e3b 100644
--- a/microdroid_manager/src/instance.rs
+++ b/microdroid_manager/src/instance.rs
@@ -332,4 +332,5 @@
     pub name: String,
     pub public_key: Vec<u8>,
     pub root_digest: Vec<u8>,
+    pub last_update_seconds: u64,
 }