config/network: Prepare for multiple networks

This commit futures proofs the code to allow for usage of more than one
docker network.

internal/config/docker.go

@@ -1,6 +1,15 @@
 package config
 
 type DockerConfig struct {
-	// name of docker network to use
-	Network string `yaml:"network" default:"distillery" validate:"nonempty"`
+	NetworkPrefix string `yaml:"network" default:"distillery" validate:"nonempty"`
+}
+
+// Networks returns a list of all docker networks to be created for purposes of the distillery.
+func (dc DockerConfig) Networks() []string {
+	return []string{dc.Network()}
+}
+
+// Network returns the name of the default network to attach all docker containers to.
+func (dc DockerConfig) Network() string {
+	return dc.NetworkPrefix
 }