feat: make nlohmann a required dependency

Author: mpeddada1

cmake/IncludeNlohmannJson.cmake

@@ -15,20 +15,7 @@
 # ~~~
 
 function (find_nlohmann_json)
-    find_package(nlohmann_json CONFIG QUIET)
-    if (nlohmann_json_FOUND)
-        return()
-    endif ()
-    # As a fall back, try finding the header. Since this is a header-only
-    # library that is all we need.
-    find_path(GOOGLE_CLOUD_CPP_NLOHMANN_JSON_HEADER "nlohmann/json.hpp"
-              REQUIRED)
-    add_library(nlohmann_json::nlohmann_json UNKNOWN IMPORTED)
-    set_property(
-        TARGET nlohmann_json::nlohmann_json
-        APPEND
-        PROPERTY INTERFACE_INCLUDE_DIRECTORIES
-                 ${GOOGLE_CLOUD_CPP_NLOHMANN_JSON_HEADER})
+    find_package(nlohmann_json CONFIG REQUIRED)
 endfunction ()
 
 find_nlohmann_json()