Keep only one build_embedding tool and move all custom DC logic/path logic to admin/html.py

[shifucun]

Major changes:

• Put most custom DC specific constants, path, logic into admin/html.py. As this is the "offline import manager", it makes sense to let it decide on all these params and pass to scripts in different stages.
• Make build_embeddings.py a general tool that can be purely self contained.
• Support catalog_dict and catalog_paths when reading catalog.
• In custom DC docker, put catalog.yaml as the same path as the GKE deployment, to unify the paths.

[shifucun]

thanks for the review!