Add Atlas Cloud config example

[binyangzhu000-sudo]

Summary

• add an Atlas Cloud community provider configuration example
• link the example from the config examples index
• keep the PR scoped to docs/config_example/ per the repository's community example guidance

Validation

• Parsed the Markdown JSON example with JSON.parse
• git diff --check
• Checked the Atlas Cloud public model catalog endpoint with a browser user agent; it returned 419 model ids and included qwen/qwen3.5-flash and deepseek-ai/deepseek-v4-pro

Notes

• No root README changes.
• No sponsor block, logo placement, credits, partner copy, or promotional section added.
• The example includes the repository's requested provider-specific non-affiliation disclaimer and does not include secrets.

[yuhp]

Thanks for the contribution. Before merging, could you please help with the following?

1. Confirm the model-list endpoint
   The example uses https://api.atlascloud.ai/v1 as the baseURL and /models as the discovery endpoint, which results in:
   https://api.atlascloud.ai/v1/models
   The Notes section currently refers to /v1/models. Could you please confirm the intended full URL and update the configuration or documentation so they are consistent?

2. Consider models.dev metadata enrichment
   Could you also evaluate whether adding the following would be appropriate?
   "modelInfoFormat": "models.dev"
   It can provide discovered models with metadata such as reasoning, tool-calling, and modality support. Since Atlas Cloud may return provider-prefixed or reseller model IDs, please first confirm that the returned IDs map well to the models.dev catalog.

Thank you!