feat(bootloader): add an example that implements multiboot

Add a new example for the bootloader that shows how to override it to implement multiboot.

examples/custom_bootloader/bootloader_multiboot/pytest_custom_bootloader_multiboot.py

@@ -0,0 +1,21 @@
+# SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+# SPDX-License-Identifier: CC0-1.0
+import pytest
+from pytest_embedded import Dut
+from pytest_embedded_idf.app import IdfApp
+
+
+@pytest.mark.esp32c3
+@pytest.mark.esp32s3
+@pytest.mark.generic
+def test_custom_bootloader_multiboot_example(app: IdfApp, dut: Dut) -> None:
+    # Expect to see all three partitions in the list
+    dut.expect_exact('default')
+    dut.expect_exact('hello_world')
+    dut.expect_exact('console')
+    # Send "down arrow" signal to select the second image, which should be `hello_world`
+    dut.write('\x1b[B')
+    # Send Enter to validate and start the image
+    dut.write('\n')
+    # Make sure the example booted properly
+    dut.expect('Hello world!')