feat: Add guest execution agent and vsock support

- Introduced a standalone guest execution agent to facilitate command execution within the guest VM over Firecracker's vsock.
- Enhanced FirecrackerClient to support vsock configuration, validating guest CID and UDS path.
- Updated configuration to include vsock settings by default.
- Refactored FirecrackerProcessManager to manage runtime sockets more effectively.
- Implemented guest agent installation and provisioning in the image store.
- Added API endpoints for executing commands in the VM and installing the guest agent.
- Improved error handling for guest execution failures and agent availability.

tests/test_install.py

@@ -216,13 +216,14 @@ class UbuntuBuildRunner:
                 return CommandResult(args, 100, stdout="Reading package lists...\n", stderr="E: unmet guest dependencies\n")
             status = "\n\n".join(
                 f"Package: {package}\nStatus: install ok installed\nVersion: 1.0"
-                for package in ("apt", "sudo", "openssh-server", "systemd-sysv")
+                for package in ("apt", "sudo", "openssh-server", "systemd-sysv", "python3")
             ) + "\n"
             files = {
                 "etc/sudoers": "root ALL=(ALL:ALL) ALL\n",
                 "etc/ssh/sshd_config": "UsePAM yes\n",
                 "etc/ssh/ssh_host_rsa_key": "template host key",
                 "usr/bin/sudo": "sudo binary",
+                "usr/bin/python3": "python binary",
                 "usr/sbin/sshd": "sshd binary", "usr/lib/systemd/systemd": "init binary",
                 "var/lib/dpkg/status": status,
                 "var/lib/dpkg/info/sudo.list": "/usr/bin/sudo\n",
@@ -319,6 +320,7 @@ class UbuntuRootfsBuildTests(unittest.TestCase):
                 self.assertLess(runner.calls.index(bootstrap), runner.calls.index(packages))
                 self.assertIn("sudo", packages)
                 self.assertIn("openssh-server", packages)
+                self.assertIn("python3", packages)
                 self.assertIn("--mount-proc", packages)
                 self.assertIn("--kill-child", packages)
                 self.assertEqual(settings.rootfs_image.stat().st_mode & 0o777, 0o600)
@@ -335,6 +337,8 @@ class UbuntuRootfsBuildTests(unittest.TestCase):
                 self.assertEqual(guest("cat /var/lib/dpkg/info/sudo.list").stdout, "/usr/bin/sudo\n")
                 self.assertRegex(guest("stat /usr/bin/sudo").stdout, r"Mode:\s+0?4755")
                 self.assertEqual(guest("cat /etc/uvm-image").stdout, _ROOTFS_RECIPE)
+                self.assertIn("socket.AF_VSOCK", guest("cat /usr/lib/uvm/agent.py").stdout)
+                self.assertIn("Delegate=yes", guest("cat /etc/systemd/system/uvm-agent.service").stdout)
                 self.assertIn("nameserver 1.1.1.1", guest("cat /etc/resolv.conf").stdout)
                 self.assertIn("KeepConfiguration=yes", guest("cat /etc/systemd/network/10-uvm.network").stdout)
                 self.assertIn("jammy-security main universe", guest("cat /etc/apt/sources.list").stdout)