Implement Python Registry Server

[tokoko]

Is your feature request related to a problem? Please describe.
Different registry implementations are python-based that makes it hard to interact with registry objects from non-python applications. For example, Java-based feature server is still unable to use sql-based registry despite sql-based registry being recommended for production use. File-based registries are supported but necessitated reimplementation of feature registry logic in Java.

Describe the solution you'd like
Implement python-based registry server that will wrap the chosen registry calls into as a grpc server similar to how python-based feature server wraps calls to online store. The solution would simplify the development of non-python applications that can directly integrate with feature server rather than having to reimplement registry logic in the language of choice.

Registry server might introduce some operational overhead, but will still be lightweight enough. Performance benefits offered by ease of use from apps like java feature server will most likely offset this operational overhead.