doc: move dns.promises to stable status

PR-URL: https://github.com/nodejs/node/pull/26592


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Signed-off-by: Beth Griggs <Bethany.Griggs@uk.ibm.com>