MB-43025: Rename kv_dcp_total_bytes_bytes

Renames the Prometheus metric kv_dcp_total_bytes_bytes to
kv_dcp_total_data_size_bytes to avoid repetition and add clarity.

Change-Id: Ifeb96ab0c91b351be934ee1df8b7b2321694e5d9
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/141249
Reviewed-by: Dave Rigby <[email protected]>
Tested-by: Build Bot <[email protected]>

Author: jameseh96

include/statistics/stats.def.h

@@ -512,7 +512,7 @@ STAT(connagg_items_remaining,
 STAT(connagg_total_bytes,
      "{connection_type}:total_bytes",
      bytes,
-     dcp_total_bytes, )
+     dcp_total_data_size, )
 STAT(connagg_total_uncompressed_data_size,
      "{connection_type}:total_uncompressed_data_size",
      bytes,