feat(router): permit log service name to be configured via env var

[brokenpip3]

This PR will make the "service" value in router logs configurable through an env var, while keeping the current hardcoded @wundergraph/router as the default. I was not able to find any existing test for router/cmd/main.go, in case you prefer I can add a couple of test cases to cover this change.

@coderabbitai summary

Checklist

• [ ] I have discussed my proposed changes in an issue and have received approval to proceed.
• [x] I have followed the coding standards of the project.
• [ ] Tests or benchmarks have been added or updated.
• [ ] Documentation has been updated on https://github.com/wundergraph/cosmo-docs.
• [x] I have read the Contributors Guide.

close: #2277