[Enhancement] (nereids)implement showCreateCatalogCommand in nereids

[LiBinfeng-01]

showCreateCatalog command is supported in legacy planner but not in nereids(new doris fe planner). you need implement the following showCreateCatalog command in nereids:
unsupportedshowCreateCatalogStatement
SHOW CREATE CATALOG name=identifier

[msridhar78]

@starocean999 @LiBinfeng-01 Please assign this issue to me