Add a redirect stub for the Hipchat page
Adds a redirect stub for the Hipchat page. Related to gitlab-docs!1643 (merged) where we're also removing the page from the left nav. Labeling as docs-technical-debt because !57556 (merged) merged without a TW reviewing it - we would've caught the deletion.
Related issues
Related to #27954 (closed)
Edited by Amy Qualls