CMake package should add the modules to CMAKE_MODULE_PATH

Right now aws-c-event-stream needs a lot of boilerplate code to determine the modules installation path while the aws-c-common package should provide it.
This would fix awslabs/aws-c-event-stream#15 simply by moving `find_package(aws-c-common)` before the various module `include`s
Using `configure_package_config_file` makes it easier to have a relocatable package.

CMakeLists.txt

@@ -25,6 +25,7 @@ include(AwsFeatureTests)
 include(AwsSanitizers)
 include(AwsThreadAffinity)
 include(AwsSIMD)
+include(CMakePackageConfigHelpers)
 include(CTest)
 
 set(GENERATED_ROOT_DIR "${CMAKE_CURRENT_BINARY_DIR}/generated")
@@ -228,9 +229,16 @@ endforeach()
 
 aws_prepare_shared_lib_exports(${PROJECT_NAME})
 
-configure_file("cmake/${PROJECT_NAME}-config.cmake"
+set(AWS_MODULE_INSTALL_DIR "${LIBRARY_DIRECTORY}/cmake")
+
+configure_package_config_file(
+  "cmake/${PROJECT_NAME}-config.cmake"
   "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}-config.cmake"
-  @ONLY)
+  INSTALL_DESTINATION "${LIBRARY_DIRECTORY}/${PROJECT_NAME}/cmake"
+  PATH_VARS AWS_MODULE_INSTALL_DIR
+  # Imported targets do not require the following macros
+  NO_SET_AND_CHECK_MACRO
+  NO_CHECK_REQUIRED_COMPONENTS_MACRO)
 
 if (BUILD_SHARED_LIBS)
    set (TARGET_DIR "shared")
@@ -260,7 +268,7 @@ list(APPEND EXPORT_MODULES
     )
 
 install(FILES ${EXPORT_MODULES}
-        DESTINATION "${LIBRARY_DIRECTORY}/cmake"
+        DESTINATION "${AWS_MODULE_INSTALL_DIR}"
         COMPONENT Development)
 
 # This should come last, to ensure all variables defined by cmake will be available for export

cmake/aws-c-common-config.cmake

@@ -1,3 +1,7 @@
+@PACKAGE_INIT@
+
+list(APPEND CMAKE_MODULE_PATH "@PACKAGE_AWS_MODULE_INSTALL_DIR@")
+
 set(THREADS_PREFER_PTHREAD_FLAG ON)
 
 if(WIN32 OR UNIX OR APPLE)