Separate Catch2Config from targets

This lets us add the installed helper scripts to the cmake module
path, letting CMake users just include them after requiring Catch2
package.

CMake/Catch2Config.cmake.in

@@ -0,0 +1,10 @@
+@PACKAGE_INIT@
+
+
+# Avoid repeatedly including the targets
+if(NOT TARGET Catch2::Catch2)
+    # Provide path for scripts
+    list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
+
+    include(${CMAKE_CURRENT_LIST_DIR}/Catch2Targets.cmake)
+endif()