add other artifacts link

this pr adds a 'other artifacts' link in the 'about artifacts' [page](https://docs.getdbt.com/reference/artifacts/dbt-artifacts) 

Resolves #4370

website/docs/reference/artifacts/dbt-artifacts.md

@@ -48,3 +48,6 @@ In the manifest, the `metadata` may also include:
 #### Notes:
 - The structure of dbt artifacts is canonized by [JSON schemas](https://json-schema.org/), which are hosted at **schemas.getdbt.com**.
 - Artifact versions may change in any minor version of dbt (`v1.x.0`). Each artifact is versioned independently.
+
+## Related docs
+- [Other artifacts](/reference/artifacts/other-artifacts) files such as `index.html` or `graph_summary.json`.