1. not collect partition stats anymore
2. merge insert of stats
3. delete period collector since it is useless
4. remove enable_auto_sample
5. move some config related to stats to global session variable
Before this PR, when analyze a table, the insert count equals column count times 2
After this PR, insert count of analyze table would reduce to column count / insert_merge_item_count.
According to my test, when analyzing tpch lineitem, the insert sql count is 1