[Bug]: linter rule should report warning if miss description in `@service` decorator

### Describe the bug

we have a linter rule `@azure-tools/typespec-azure-core/documentation-required` to require documentation, however if we we miss docs on `@service` decorator, it will not report any warning.

### Reproduction

[playground](https://cadlplayground.z22.web.core.windows.net/cadl-azure/?c=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%2B5QDbLi7pAIHkAXNQYXJhbWV0ZXLJMT47xGEvKirKX3DJRCAqL898ymDFX8Q4QWdlIG9mIGXIPyovCiAgYWdlPzogaW50MzI7CscpQ2l0edIqY2l0eT86IHN0cuUCVccsUHJvZmls01lAZW5jb2RlKCJiYXNlNjR1cmwi5AE7cMYwPzogYnl0ZXPJSFRoZSBzdGF0dXPES3RoZSBsYXN0IOQAxWF0aW9uLsdWdmlzaWJpbGl0eSgicmVhZMhVxBjlAu9TdGF0xF%2FlAkzMFOkBQMRrzDLFeOUAwmEg6AOExW9AbHJvxDt1cwp1bmlvbtJU5QFc5gESLOwAyshHIGNyZcQncmVxdWVzdCBoYXMgYmVlbiBhY2NlcHRlZMRnICBBxw46ICLICyLWUGnEQOQAtOkAwchE7ACcOiAizA%2FaTHVwZGF0xE%2FFQ1XHDjogIsgLyjvoAp7qAMTmANxk5wGaU3VjY2VlZOUAxckM0z%2FFNuQBTWZhaWzJPkbFDTogIsYJ3Dh3YXMgY2FuY2XKPkPHD%2BQEkccL%2FwFAIGRlbGXpAYBExA3mAPnIC%2BQEwe8Db21vduoByukDcU1vdmVSxxXoA2rEc21vdsRoZnJvbSBsb2PmALzFbsQT8QNIyzN0b88xdG%2FKL%2FcAlXNwb25z5QN67ACWxxbsAJfuA2TFPsVkxnzmAu7NbmludGVyZuQFr0%2FoA4xzIGV4dGVuZHP2BkIuyyl7feYGT8gjyhvLWegAzeYEq2dldOQBp0HKNVJlYWTsBQgg5wJ7T3LlAqflAdbLL0PHHVJlcGxhY2VBc3luY84%2F5QL30DdQYXRjaFPMLCzzBU7FQOYCPc9A5QI6ZVdpdGhvdXRPa9N3bGlzdEJ5yDBHcm91cM9ETMUiUGFyZW501DxTdWJzY3JpcOUCHMY7xjPMGcw56AX7IHNhbXBs6wMJYWPFRHRoYXTmAgbpBb50byBkaWZmZeQAhO8CicUp7gCyQcVI7wE36wMUyA3mAovzAJJIRUFE6gXnxH5jaGVja%2BoAqmV4aXN0ZW5j6AaHxB5FyRTvAfvNHe4HPA%3D%3D&e=%40azure-tools%2Ftypespec-autorest&options=%7B%22linterRuleSet%22%3A%7B%22extends%22%3A%5B%22%40azure-tools%2Ftypespec-azure-rulesets%2Fresource-manager%22%5D%7D%7D)

### Checklist

- [X] Follow our [Code of Conduct](https://github.com/azure/typespec-azure/blob/main/CODE_OF_CONDUCT.md)
- [X] Check that this issue is about the Azure libraries for typespec. For bug in the typespec language or core libraries file it in the [TypeSpec repo](https://github.com/Microsoft/TypeSpec/issues/new/choose)
- [X] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
- [X] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.

Start with the @azure-tools/typespec-azure-core/documentation-required linter rule and use the linked TypeSpec Azure playground reproduction to observe how a missing @service description is handled. Done means the rule reports a warning when the @service decorator lacks documentation, while preserving its existing behavior for other declarations.

Written by the indexing model from the issue text.