Add support for OpenZeppelin sort-pair verifcation

[txaty]

Add SortSiblingPair parameter in Config for OpenZeppelin support:

• If it is set to true, then the sibling hash pairs are first sorted in ascending order, and then concatenated.
• Otherwise, no change.

This PR is originated from https://github.com/txaty/go-merkletree/pull/20 by user dev-ubq.

[codecov[bot]]

Codecov Report

Merging #21 (413e634) into main (6ccb37a) will increase coverage by 0.39%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #21      +/-   ##
==========================================
+ Coverage   92.12%   92.51%   +0.39%     
==========================================
  Files           2        2              
  Lines         457      481      +24     
==========================================
+ Hits          421      445      +24     
  Misses         24       24              
  Partials       12       12              

Impacted Files	Coverage Δ
merkle_tree.go	92.38% <100.00%> (+0.40%)	:arrow_up:

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