Document: Substreams is deprecating Substreams-Powered Subgraphs, please update the doc and suggest a replacement

This is the [PR](https://github.com/streamingfast/substreams/pull/630/files) to remove SpS, it's released in [v1.15.7](https://github.com/streamingfast/substreams/releases/tag/v1.15.7). And in the document (https://thegraph.com/docs/en/substreams/sps/introduction/), the link https://docs.substreams.dev/how-to-guides/sinks/subgraph/graph-out is no longer present in the substreams documentation. After SpS is deprecated, what is the replacement for SpS?