test(examples/security): Add an example to demonstrate signing using Key Manager keys

examples/security/key_manager/CMakeLists.txt

@@ -0,0 +1,8 @@
+# The following lines of boilerplate have to be in your project's
+# CMakeLists in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.22)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+# "Trim" the build. Include the minimal set of components, main, and anything it depends on.
+idf_build_set_property(MINIMAL_BUILD ON)
+project(key_manager)