Support append mode by default for MOR table with INSERT operation

1. Insert scenario in the COW table, if both online sync-clustering and online async-clustering(plan generate || plan execute) are configured simultaneously, sometimes sync-clustering takes effect, sometimes async-clustering takes effect：

sync-clustering=true & generate async-clustering=true & execute async-clustering=true：sync-clustering takes effect
sync-clustering=true & generate async-clustering=false & execute async-clustering=true: async-clustering takes effect

1. Insert scenario in the MOR table，sometimes generate log files, sometimes generate parquet files.
   async-compaction=true & generate async-clustering=false : generate log files
   async-compaction=false & generate async-clustering=true: generate parquet files

This will cause confusion for users

After modification:

1. Insert scenario in the COW table, sync-clustering has higher priority than online async-clusering.
2. Insert scenario in the MOR table will always generate parquet files