chore: add PAIMON_THIRDPARTY_MIRROR_URL env

Author: lucasfang

cmake_modules/ThirdpartyToolchain.cmake

@@ -61,7 +61,11 @@ foreach(_VERSION_ENTRY ${TOOLCHAIN_VERSIONS_TXT})
     set(${_VARIABLE_NAME} ${_VARIABLE_VALUE})
 endforeach()
 
-set(THIRDPARTY_MIRROR_URL "")
+if(DEFINED ENV{PAIMON_THIRDPARTY_MIRROR_URL})
+    set(THIRDPARTY_MIRROR_URL "$ENV{PAIMON_THIRDPARTY_MIRROR_URL}")
+else()
+    set(THIRDPARTY_MIRROR_URL "")
+endif()
 
 if(DEFINED ENV{PAIMON_ARROW_URL})
     set(ARROW_SOURCE_URL "$ENV{PAIMON_ARROW_URL}")