Enlarge field number limitation (#12517)

Signed-off-by: Nyhmo <yihua.mo@zilliz.com>

configs/milvus.yaml

@@ -87,7 +87,7 @@ proxy:
     timeTick:
       bufSize: 512
   maxNameLength: 255  # max name length of collection or alias
-  maxFieldNum: 64     # max field number of a collection
+  maxFieldNum: 256     # max field number of a collection
   maxDimension: 32768 # Maximum dimension of vector
   maxShardNum: 256 # Maximum number of shards in a collection
   maxTaskNum: 1024 # max task number of proxy task queue