Add support for numbered databases

[adam-fowler]

• Add database number to ValkeyClientConfiguration
• Add database number to ValkeyConnectionConfiguration and pass from client to connection
• Add database number to ValkeyChannelHandler.Configuration and pass from connection
• In ValkeyChannelHandler.setConnected if database number is non-zero add SELECT call to list of commands called after the HELLO command. This should be done in a similar manner to Add support for calling READONLY on replicas #255.