Is your feature request related to a problem? Please describe.
Currently, for grpc WriteToOnlineRequest, features map is written as Map<String, String> to feast feature server. This makes it impossible to write any complex types (array, map, struct).

Describe the solution you'd like
We should be able to alternatively write Map<String, ValueProto> to feast feature server for writes.

Describe alternatives you've considered
Possibly write JSON formatted strings but would require client to serialize and server to deserialize which is wasteful from PROTO perspective