Added CMake warning if Update Client Hub is selected (#78)

* added warning if UCHub is selected

* corrected warning

* Updated UC hub warning text

Co-authored-by: Yash  Goyal <yashgoyal@C02Y71AJJGH5.local>

Author: Prakhar Bhatt

cmake/edge_configure.cmake

@@ -167,6 +167,7 @@ if (${FIRMWARE_UPDATE})
      MESSAGE("Update client hub selected.")
      add_definitions ("-DMBED_CLOUD_CLIENT_SUPPORT_UPDATE=1")
      add_definitions("-DPAL_DNS_API_VERSION=1")
+     message("WARNING: The next release, 0.20, will deprecate the Update Client (UC) hub library. Please use the new FOTA framework library, which can be enabled by adding -DFOTA_ENABLE=ON flag.")
      set(ENABLE_UC_HUB ON)
   endif()