Support convertion from []interface to list type.

[ariefrahmansyah]

What this PR does / why we need it:

Given a first successful standard transformer request that has feast feature retrieval with list types:

➜ curl -X POST http://localhost:8081/v1/models/echo:predict -d '{"driver_id":1}'
{"merlin":[{"merlin_test_driver_features:test_double":3.14,"merlin_test_driver_features:test_double_list":[1.23,2.34,3.45],"merlin_test_driver_features:test_int64":null,"merlin_test_driver_features:test_int64_list":null,"merlin_test_driver_features:test_string":null,"merlin_test_driver_features:test_string_list":["AAABBBCCC"],"merlin_test_driver_id":"1"}]}

And feast cache is enabled, and we send the same request, it will return error:

➜ curl -X POST http://localhost:8081/v1/models/echo:predict -d '{"driver_id":1}'
{"code":500,"message":"preprocessing error: error executing preprocessing operation: *pipeline.FeastOp: unsupported conversion from []interface {} to []float64"}

This is because, on the second request, standard transformer uses cached feature value which stored as []interface instead of the correct Feast's list type.

Checklist

• Added unit test, integration, and/or e2e tests
• Tested locally

[pradithya]

Can you add test that reproduce the issue, those new unit tests seems didn't cover the bug.

[pradithya]

Can you also handle it in feature cache (https://github.com/gojek/merlin/blob/a382020bfa5f660467103a21d68b12b78c8f47ef/api/pkg/transformer/feast/feature_cache.go#L159) so that anything return by cache is already correct.

It's currently called castIntValue since it's only for handling int, but it seems necessary to handle the list type conversion there too.

[pradithya]

Awesome! LGTM!

[tiopramayudi]

LGTM