Improve index bloat estimation

[alexeyklyukin]

We had an index that was shown as 0,3 bloat ratio (meaning 0,3%) and 0 bytes to win by the PGObserver estimator, while the estimate at https://github.com/ioguix/pgsql-bloat-estimation/blob/master/btree/btree_bloat.sql shown it as 50% bloated.

After creating the new index with the same parameters it was indeed shown to be smaller than the original one. (the original one was 18GBs, and the replacement took only 7GB). Therefore, it looks like the bloat estimator needs to be re-examined.