Refactor retrievePreviousBuild and buildManifest library

[zelinh]

Description

Move the latest index download to the buildManifest library. Now if the latest index is not available, we would run the full build without incremental.

Issues Resolved

https://github.com/opensearch-project/opensearch-build-libraries/issues/392

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov[bot]]

Codecov Report

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

Project coverage is 87.06%. Comparing base (0721e85) to head (78ecbe0).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #396 +/- ## ============================================ + Coverage 87.01% 87.06% +0.05% Complexity 31 31 ============================================ Files 86 87 +1 Lines 231 232 +1 Branches 12 12 ============================================ + Hits 201 202 +1 Misses 22 22 Partials 8 8 ```

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[opensearch-trigger-bot[bot]]

The backport to 6.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/backport-6.x 6.x
# Navigate to the new working tree
pushd ../.worktrees/backport-6.x
# Create a new branch
git switch --create backport/backport-396-to-6.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 5a9bd970870c3b6c4c5500cc27d5c54d56b4f818
# Push it to GitHub
git push --set-upstream origin backport/backport-396-to-6.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-6.x

Then, create a pull request where the base branch is 6.x and the compare/head branch is backport/backport-396-to-6.x.