[Enhancement] (nereids)implement showDataTypesCommand in nereids

[LiBinfeng-01]

showDataTypes command is supported in legacy planner but not in nereids(new doris fe planner). you need implement the following showDataTypes command in nereids:
unsupportedshowDataTypesStatement
SHOW DATA TYPES

[msridhar78]

@starocean999 @LiBinfeng-01 I will pick this up. Thanks