guest: debian: Implement storage_balloon_agent

Add storage_balloon_agent daemon in Debian and its client in
the TerminalApp for enabling storage ballooning.
This feature is hidden behind a feature flag 'terminalStorageBalloon'.

Since we still use non-sparse disks, the balloon shouldn't affect
the guest's disk space yet.

Bug: 382174138
Test: Run a VM and check logs

Change-Id: I75d926bb8aa8a02bf635e94e35715e5aa23c8090
diff --git a/build/debian/build.sh b/build/debian/build.sh
index 9c4d4b1..8c1345c 100755
--- a/build/debian/build.sh
+++ b/build/debian/build.sh
@@ -204,6 +204,7 @@
 	build_rust_as_deb forwarder_guest
 	build_rust_as_deb forwarder_guest_launcher
 	build_rust_as_deb shutdown_runner
+	build_rust_as_deb storage_balloon_agent
 }
 
 package_custom_kernel() {