Support for typed features in grpc write request

**Is your feature request related to a problem? Please describe.**
Currently, for grpc WriteToOnlineRequest, features map is written as Map 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 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