[Discuss] Support different stores for different projects in one single feast-serving container

Move the discussion from slack to github issue for visibility.

We have a use case that require using different redis clusters for different projects, e.g. shared features can be placed in a shared redis cluster and team-specific features can be placed in team redis cluster. We will have a single request that read from multiple clusters.

If we think this is the direction moving forward, we can brainstorm implementation details here.