model: datalake_coordinator batch type

For use by the upcoming datalake coordinator STM to track files that
need to be committed to Iceberg.

src/v/model/model.cc

@@ -388,6 +388,8 @@ std::ostream& operator<<(std::ostream& o, record_batch_type bt) {
         return o << "batch_type::group_fence_tx";
     case record_batch_type::partition_properties_update:
         return o << "batch_type::partition_properties_update";
+    case record_batch_type::datalake_coordinator:
+        return o << "batch_type::datalake_coordinator";
     }
 
     return o << "batch_type::unknown{" << static_cast<int>(bt) << "}";

src/v/model/record_batch_types.h

@@ -54,7 +54,8 @@ enum class record_batch_type : int8_t {
     group_fence_tx = 33,      // fence batch in group transactions
     partition_properties_update
     = 34, // special batch type used to update partition properties
-    MAX = group_fence_tx,
+    datalake_coordinator = 35, // datalake::coordinator::*
+    MAX = datalake_coordinator,
 };
 
 std::ostream& operator<<(std::ostream& o, record_batch_type bt);