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/avf_flags.aconfig b/build/avf_flags.aconfig
index 921c374..571c359 100644
--- a/build/avf_flags.aconfig
+++ b/build/avf_flags.aconfig
@@ -16,4 +16,12 @@
   namespace: "virtualization"
   description: "Flag for GUI support in terminal"
   bug: "386296118"
+}
+
+flag {
+  name: "terminal_storage_balloon"
+  is_exported: true
+  namespace: "virtualization"
+  description: "Flag for storage ballooning support in terminal"
+  bug: "382174138"
 }
\ No newline at end of file
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() {
diff --git a/build/debian/fai_config/package_config/AVF b/build/debian/fai_config/package_config/AVF
index 3aa8ab0..f1ee065 100644
--- a/build/debian/fai_config/package_config/AVF
+++ b/build/debian/fai_config/package_config/AVF
@@ -8,6 +8,7 @@
 forwarder-guest
 forwarder-guest-launcher
 shutdown-runner
+storage-balloon-agent
 weston
 xwayland
 mesa-vulkan-drivers