[AWSCORE-697] Add versioning to llm_obs template

[dhan0779]

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What does this PR do?

This PR modifies the release script for the cloudformation llm_obs template to upload its latest version to the datadog-opensource-asset-versions bucket. The version information is stored in llm_obs/versions.json:

{
  "latest": {
    "version": "v1.0.0",
    "release_date": "2026-02-04"
  }
}

Motivation

What inspired you to submit this pull request?

Testing Guidelines

I tested the release script using the aws-ints-playground account:
aws-vault exec sso-aws-ints-team-playground-account-admin -- ./release.sh llm-obs-test2 --private

I verified that the version gets uploaded to a test bucket: https://us-east-1.console.aws.amazon.com/s3/buckets/datadog-opensource-asset-versions-test2?region=us-east-1&tab=objects

Additional Notes

Anything else we should know when reviewing?