[DOCS] Add data stream APIs to main API page (#58204)

Author: danhermann

docs/reference/rest-api/index.asciidoc

@@ -17,6 +17,7 @@ endif::[]
 * <<cat, cat APIs>>
 * <<cluster, Cluster APIs>>
 * <<ccr-apis,{ccr-cap} APIs>>
+* <<data-stream-apis,Data stream APIs>>
 * <<docs, Document APIs>>
 * <<enrich-apis,Enrich APIs>>
 * <<graph-explore-api,Graph Explore API>>