tests: gdbstub: Improve test case

Gdbstub test improvements: using pytest fixtures, parametrization, and
expected pattern matching on outputs from GDB and the test application.

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>

tests/subsys/debug/gdbstub/pytest/conftest.py

@@ -0,0 +1,20 @@
+#
+# Copyright (c) 2023 intel Corporation.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+import pytest
+
+def pytest_addoption(parser):
+    parser.addoption('--gdb_timeout')
+    parser.addoption('--gdb_script')
+
+@pytest.fixture()
+def gdb_script(request):
+    return request.config.getoption('--gdb_script')
+
+@pytest.fixture()
+def gdb_timeout(request):
+    return int(request.config.getoption('--gdb_timeout', default=60))
+#