Fetch cmake modules at configure-time

Instead of using a submodule. See Scott (2023 k1077, § 39.6.2 "Sharing
CMake Modules And Commands"). The drawbacks are: the directory cmake
is duplicated in each build directory; configuration requires a
network connection. The advantages are: it is easier to download the
project without git; we can more easily package a release.

.gitmodules

-[submodule "cmake"]
-	path = cmake
-	url = https://github.com/lguez/cmake

CMakeLists.txt

@@ -2,7 +2,11 @@ cmake_minimum_required(VERSION 3.20...3.27)
 project(Detection_eddies LANGUAGES Fortran)
 set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS Debug Release Profile
   RelWithDebInfo)
-list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/cmake")
+include(FetchContent)
+FetchContent_Declare(LG_cmake_utils GIT_REPOSITORY
+  https://gitlab.in2p3.fr/guez/cmake.git GIT_TAG 517d97c3)
+FetchContent_MakeAvailable(LG_cmake_utils)
+list(APPEND CMAKE_MODULE_PATH "${lg_cmake_utils_SOURCE_DIR}")
 find_package(NetCDF_Fortran REQUIRED)
 find_package(MPI)
 

cmake @ c49b86c3

-Subproject commit c49b86c38a01ab90b665f41d0cc606f499157eae