Registry proto doesn't support multiple Infra objects

[achals]

Expected Behavior

the Registry proto should support multiple infra objects, per project, similar to feature views/entities/data sources/etc.

Current Behavior

https://github.com/feast-dev/feast/blob/master/protos/feast/core/Registry.proto#L49 The Registry only allows a single Infra object.

Possible Solution

Change the registry proto to a repeated field, and add project id to the Infra object message.