Support multiple CDC endpoints

Is your feature request related to a problem? Please describe. For a purely on-prem distributed app with multiple clusters, I need to sync data between the clusters (albeit with eventual consistency) using bidirectional CDC streaming directly between leaders of each cluster. As currently only one CDC endpoint is supported, one leader can stream to at most one other cluster leader.

Describe the solution you'd like Enable CDC streaming to multiple endpoints. Then a local CDC consumer service at each leader node can receive the CDC streams from other clusters and apply the SQL to the local leader via the /db/execute API.

Describe alternatives you've considered The local CDC consumer will relay the CDC stream to other cluster leaders. Adds complexity and duplication (manage event queue, etc.) Much easier for rqlite to enable multiple endpoints, I guess.