[BUG] Plugin helpers fix related to fs promises module

[kavilla]

Description

In Node v10, there was no dedicated module for fs/promises. Causing the plugin helpers to fail while building out plugins.

Solved by importing promises from fs then using the desired methods.

Signed-off-by: Kawika Avilla kavilla414@gmail.com

Issues Resolved

#2485

Check List

• All tests pass
  • yarn test:jest
  • yarn test:jest_integration
  • yarn test:ftr
• New functionality includes testing.
• New functionality has been documented.
• Update CHANGELOG.md
• Commits are signed per the DCO using --signoff

[kavilla]

integ passed locally and unit tests seem to be passing. due to the nature of this, will merge in.

[opensearch-trigger-bot]

The backport to 1.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-1.x 1.x
# Navigate to the new working tree
cd .worktrees/backport-1.x
# Create a new branch
git switch --create backport/backport-2486-to-1.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 945cfe65ff7042ba27cffd798b6b627e7b89fa5d
# Push it to GitHub
git push --set-upstream origin backport/backport-2486-to-1.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-1.x

Then, create a pull request where the base branch is 1.x and the compare/head branch is backport/backport-2486-to-1.x.