[Backport 6.x] Add a new groovy library to download the previous build artifacts

[opensearch-trigger-bot[bot]]

Backport 8b7df1261220a27f90f1ac7042f8c5256540597c from #362.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (513eb9c) 86.04% compared to head (b0b76b5) 86.11%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## 6.x #365 +/- ## ============================================ + Coverage 86.04% 86.11% +0.06% Complexity 29 29 ============================================ Files 81 82 +1 Lines 215 216 +1 Branches 12 12 ============================================ + Hits 185 186 +1 Misses 22 22 Partials 8 8 ```

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