test: add ipc test to test multiprocess type conversion code

Add unit test to test IPC method calls and type conversion between bitcoin c++
types and capnproto messages.

Right now there are custom type hooks in bitcoin IPC code, so the test is
simple, but in upcoming commits, code will be added to convert bitcoin types to
capnproto messages, and the test will be expanded.

src/test/ipc_tests.cpp

@@ -0,0 +1,13 @@
+// Copyright (c) 2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <test/ipc_test.h>
+#include <boost/test/unit_test.hpp>
+
+BOOST_AUTO_TEST_SUITE(ipc_tests)
+BOOST_AUTO_TEST_CASE(ipc_tests)
+{
+    IpcTest();
+}
+BOOST_AUTO_TEST_SUITE_END()