test: Connect test unit to console when running interactively

When running interactively, let's connect the test unit directly
to the console. This enables adding "bash" anywhere within an
integration test to get a shell within the test environment.

test/integration-test-wrapper.py

@@ -456,6 +456,16 @@ def main() -> None:
             [Unit]
             Wants=multi-user.target getty-pre.target
             Before=getty-pre.target
+
+            [Service]
+            StandardInput=tty
+            StandardOutput=inherit
+            StandardError=inherit
+            TTYReset=yes
+            TTYVHangup=yes
+            IgnoreSIGPIPE=no
+            # bash ignores SIGTERM
+            KillSignal=SIGHUP
             """
         )