feat: move elevation map loader (#740)

[wep21]

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[tkimura4]

LGTM

[tkimura4]

/_w/autoware.universe/autoware.universe/perception/elevation_map_loader/src/elevation_map_loader_node.cpp: In member function ‘void ElevationMapLoaderNode::onMapHash(autoware_external_api_msgs::msg::MapHash<std::allocator >::SharedPtr)’:
/w/autoware.universe/autoware.universe/perception/elevation_map_loader/src/elevation_map_loader_node.cpp:126:45: error: ‘using element_type = struct autoware_external_api_msgs::msg::MapHash<std::allocator >’ {aka ‘struct autoware_external_api_msgs::msg::MapHash<std::allocator >’} has no member named ‘pcd’
126 | const auto elevation_map_hash = map_hash->pcd;

[tkimura4]

This PR depends on
#140