Expose version of GetClusterConfig

[Yoav Tock]

pkg/bcdb/config_tx_context.go

// GetClusterConfig returns the current cluster config.
// A ConfigTxContext only gets the current config once, subsequent calls return a cached value.
// The value returned is a deep clone of the cached value and can be manipulated.
GetClusterConfig() (*types.ClusterConfig, error)

Add the version to the return arguments:

GetClusterConfig() (*types.ClusterConfig, Version, error)

[Yoav Tock]

#174