ORC-1810: [C++] Add environment variable ORC_FORMAT_URL

### What changes were proposed in this pull request?

Add an CMake option ORC_FORMAT_URL to indicate where to download the orc-format_ep

### Why are the changes needed?

Handle the issue discussed apache/arrow#43417

### How was this patch tested?

Test it locally

### Was this patch authored or co-authored using generative AI tooling?

NO

Closes #2094 from luffy-zh/ORC-1810.

Authored-by: luffy-zh <zhnice@outlook.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: luffy-zh

cmake_modules/ThirdpartyToolchain.cmake

@@ -136,8 +136,15 @@ endfunction()
 
 # ----------------------------------------------------------------------
 # ORC Format
+if(DEFINED ENV{ORC_FORMAT_URL})
+  set(ORC_FORMAT_SOURCE_URL "$ENV{ORC_FORMAT_URL}")
+  message(STATUS "Using ORC_FORMAT_URL: ${ORC_FORMAT_SOURCE_URL}")
+else()
+  set(ORC_FORMAT_SOURCE_URL "https://www.apache.org/dyn/closer.lua/orc/orc-format-${ORC_FORMAT_VERSION}/orc-format-${ORC_FORMAT_VERSION}.tar.gz?action=download" )
+  message(STATUS "Using DEFAULT URL: ${ORC_FORMAT_SOURCE_URL}")
+endif()
 ExternalProject_Add (orc-format_ep
-  URL "https://www.apache.org/dyn/closer.lua/orc/orc-format-${ORC_FORMAT_VERSION}/orc-format-${ORC_FORMAT_VERSION}.tar.gz?action=download"
+  URL ${ORC_FORMAT_SOURCE_URL}
   URL_HASH SHA256=739fae5ff94b1f812b413077280361045bf92e510ef04b34a610e23a945d8cd5
   CONFIGURE_COMMAND ""
   BUILD_COMMAND     ""