breaking kmsg: update per protocol changes

This will break existing usages of kmsg.MetadataResponseTopic.Topic,
which is likely not used *too* much. However, this is further impetus to
just have major versions for kmsg that change anytime the protocol
breaks.

generate/definitions/03_metadata

@@ -1,5 +1,5 @@
 // MetadataRequest requests metadata from Kafka.
-MetadataRequest => key 3, max version 11, flexible v9+
+MetadataRequest => key 3, max version 12, flexible v9+
   // Topics is a list of topics to return metadata about. If this is null
   // in v1+, all topics are included. If this is empty, no topics are.
   // For v0 (<Kafka 0.10.0.0), if this is empty, all topics are included.
@@ -63,7 +63,7 @@ MetadataResponse =>
     // There can be a myriad of other errors for unsuccessful topic creation.
     ErrorCode: int16
     // Topic is the topic this metadata corresponds to.
-    Topic: string
+    Topic: nullable-string
     // The topic ID.
     TopicID: uuid // v10+
     // IsInternal signifies whether this topic is a Kafka internal topic.

pkg/kversion/kversion.go

@@ -868,8 +868,8 @@ var maxTip = nextMax(max280, func(v listenerKeys) listenerKeys {
 	// KAFKA-10580 2b8aff58b575c199ee8372e5689420c9d77357a5 KIP-516
 	v[1].inc() // 13 fetch
 
+	// KAFKA-10744 1d22b0d70686aef5689b775ea2ea7610a37f3e8c KIP-516
+	v[3].inc() // 12 metadata
+
 	return v
 })
-
-// NOTE when adding to this, be sure to update any raw usages of requests in
-// kgo (because we do not go through NewXyzRequest() to set fields).