feat: override service name by OTEL_SERVICE_NAME env

[okamototk]

Description

Override service name by OTEL_SERVICE_NAME env.

When I integrated Datadog to strands, all traces are named to "strands-agents" service and could't override by OTEL_SERVICE_NAME. This PR fix this problem.

Type of Change

• Bug fix

Testing

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.