Migrating from checkstyle to spotless for formatting

[VachaShah]

Description

Adding spotless support in this repo in place of checkstyle so that we can get features for checking and applying the formatting using spotless. The rules used here are from the OpenSearch repo. spotlessJavaCheck is now part of the build task making it easier for developers to format their changes.

This PR adds the spotless functionality, makes it part of the build and enforces spotless on 3 modules - json, transport and util along with the samples folder. The commits are divided accordingly.

Issues Resolved

List any issues this PR will resolve, e.g. Closes [...].

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.

[VachaShah]

@reta @dblock The next PRs will enable spotless for other modules. LMK what you think of this division!

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

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-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-648-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 57dc5cf1e5c2ee01fc33fe0b89e93f653c22adda
# Push it to GitHub
git push --set-upstream origin backport/backport-648-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-648-to-2.x.