doc: introduce a triager role

The role helps triaging issue backlogs effectively
Fixes: https://github.com/nodejs/node/issues/34054
Refs: https://github.com/nodejs/TSC/pull/891

PR-URL: https://github.com/nodejs/node/pull/34295


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>