benchmark-pull-request.yml Workflow Improvements.

[prudhvigodithi]

Description

benchmark-pull-request.yml Workflow Improvements.

• Restrict the workflow to opensearch-project/OpenSearch repo.
• Avoid using substring match with JSON-encoded, ensuring robustness in parsing and processing with an exact match to an element in the array.

Related Issues

NA: Workflow Improvements.

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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.

[rishabh6788]

Thanks @prudhvigodithi for hardening security of the workflow.
@reta This PR updates the username match from substring match to exact match so that any other user who matches the substring from any of the maintainer's id is not able to bypass the approval step.