[FEATURE] Allow overriding the aws service identifier in AwsSigv4Signer

[bwg]

Description

Currently the service identifier is hard coded to "es" with no way to override. This change allows for a user provided service option to override the default.

Issues Resolved

#330

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[nhtruong]

@bwg It looks good. Just need to update CHANGELOG.MD to include this change. Thank you :)

[nhtruong]

@dblock would you mind taking a look at this PR? Thanks

[dblock]

@bwg When do you need to overwrite the service identifier?

[dblock]

Btw, I merged a little fast, @bwg care to add to https://github.com/opensearch-project/opensearch-js/blob/main/USER_GUIDE.md?

[magoz]

Thank you, @bwg!
Is there a new release planned soon that includes this?

@bwg When do you need to overwrite the service identifier?

@dblock I'm using Amazon OpenSearch Serverless, which uses aoss instead of es.

[dblock]

@magoz Makes sense. I opened #356 to document support for OpenSearch Serverless. If you know of any other issues than the ones known in that for OpenSearch Serverless, please add!

[magoz]

Thanks, @dblock! Let's continue the conversation there then, I've added a new comment.

[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-333-to-1.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 2f840e54860419f76ef8354a0fe070403d437386
# Push it to GitHub
git push --set-upstream origin backport/backport-333-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-333-to-1.x.