stream: mark compose as experimental

PR-URL: #39494
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: ronag

doc/api/stream.md

@@ -1861,6 +1861,8 @@ failure, this can cause event listener leaks and swallowed errors.
 added: REPLACEME
 -->
 
+> Stability: 1 - `stream.compose` is experimental.
+
 * `streams` {Stream[]|Iterable[]|AsyncIterable[]|Function[]}
 * Returns: {stream.Duplex}