Replaced json-cmake submodule with CPM.

.gitmodules

@@ -19,9 +19,6 @@
 [submodule "ThirdParty/ogs6py"]
 	path = ThirdParty/ogs6py
 	url = https://github.com/joergbuchwald/ogs6py.git
-[submodule "ThirdParty/json-cmake"]
-	path = ThirdParty/json-cmake
-	url = https://github.com/ufz/json-cmake.git
 [submodule "ThirdParty/xdmf"]
 	path = ThirdParty/xdmf
 	url = https://gitlab.opengeosys.org/ogs/xdmflib.git

json-cmake @ 9708cb09

-Subproject commit 9708cb091f6b89b94d71ae98f8b9e68ea04c47dd

scripts/cmake/SubmoduleSetup.cmake

@@ -5,7 +5,6 @@ endif()
 # This file initializes the required submodules
 set(REQUIRED_SUBMODULES
     ThirdParty/iphreeqc/src
-    ThirdParty/json-cmake
 )
 if(OGS_USE_XDMF)
     list(APPEND REQUIRED_SUBMODULES ThirdParty/xdmf)

scripts/cmake/Versions.cmake

-include(${PROJECT_SOURCE_DIR}/ThirdParty/json-cmake/JSONParser.cmake)
+CPMAddPackage(
+    NAME json-cmake
+    GITHUB_REPOSITORY ufz/json-cmake
+    GIT_TAG 9708cb091f6b89b94d71ae98f8b9e68ea04c47dd
+    DOWNLOAD_ONLY YES
+)
+include("${json-cmake_SOURCE_DIR}/JSONParser.cmake")
 file(READ ${PROJECT_SOURCE_DIR}/web/data/versions.json jsonFileString)
 sbeParseJson(ogs jsonFileString)
 # Provides variables, e.g. ogs.minimum_version.gcc