Cache non file-based registries for python feature server

[sfc-gh-madkins]

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A considerable amount of latency occurs when retrieving data from registry when calling get_online_features()

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[jfli-thu]

Maybe we can support customize registry in feature_store.yaml firstly so that we can use customized registry cache implementation?

[jfli-thu]

it seems the amount of latency using sql registry may also relate to the unnecessary feast_metadata update when get or list metadata .

Should that init func only used by apply_objects? @adchia