examples: build system: add link-time registration plugin example

Closes https://github.com/espressif/esp-idf/issues/7682

examples/build_system/cmake/plugins/pytest_plugins.py

@@ -0,0 +1,32 @@
+# SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
+# SPDX-License-Identifier: CC0-1.0
+
+import textwrap
+
+import pytest
+from pytest_embedded import Dut
+
+
+@pytest.mark.esp32
+@pytest.mark.esp32c3
+@pytest.mark.generic
+def test_plugins(dut: Dut) -> None:
+    log_text = textwrap.dedent(r"""
+        Nihao plugin performing self-registration...
+        Successfully registered plugin 'Nihao'
+        Hello plugin performing self-registration...
+        Successfully registered plugin 'Hello'
+        cpu_start: Starting scheduler
+        List of plugins:
+        - Plugin 'Hello'
+        - Plugin 'Nihao'
+        Calling greet function of plugin 'Hello'...
+        Hello, World!
+        Done with greet function of plugin 'Hello'.
+        Calling greet function of plugin 'Nihao'...
+        你好 World!
+        Done with greet function of plugin 'Nihao'.
+    """).strip('\n')
+
+    for line in log_text.split('\n'):
+        dut.expect_exact(line.encode('utf-8'))