eg. in production there's (currently) only ASM/DB, so it's redundant to have to specify --asm

Instead the cluster would be required to start with a flag specifying the writing resolve, so the client would not make any decisions.

This change should allow the controller to support multiple providers for reading but only one for writing, as usual, but the controller is the one that selects the writer at startup. This would also remove the types for setting the provider over gRPC. The client will still need these flags for the local case, but for the gRPC path it would be able to skip requiring the user to set a writer.