roachtest/cdc/mixed-versions: use mixed version framework

This change updates the `cdc/mixed-versions` roachtest to use
the mixed version testing framework. This mixed version testing
framework is better than the previous framework because it offers
testing for multiple upgrades. It will also make it easier to
maintain and expand this cdc-specific test.

Informs: cockroachdb#107451
Epic: None
Release note: None

pkg/cmd/roachtest/tests/cdc.go

@@ -641,7 +641,7 @@ func runCDCBank(ctx context.Context, t test.Test, c cluster.Cluster) {
 		t.Fatal(err)
 	}
 
-	tc, err := kafka.consumer(ctx, "bank")
+	tc, err := kafka.newConsumer(ctx, "bank")
 	if err != nil {
 		t.Fatal(errors.Wrap(err, "could not create kafka consumer"))
 	}
@@ -2242,7 +2242,7 @@ func (k kafkaManager) createTopic(ctx context.Context, topic string) error {
 	})
 }
 
-func (k kafkaManager) consumer(ctx context.Context, topic string) (*topicConsumer, error) {
+func (k kafkaManager) newConsumer(ctx context.Context, topic string) (*topicConsumer, error) {
 	kafkaAddrs := []string{k.consumerURL(ctx)}
 	config := sarama.NewConfig()
 	// I was seeing "error processing FetchRequest: kafka: error decoding