[waffle]Add an accessibility label to the search engine choice list

Screen recording: http://b/320627808#comment12

Fixed: b:320627808
Change-Id: If386c889d819d6d218e16e9093c71d76814d9b44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5412857


Auto-Submit: Jack Yammine <jyammine@google.com>
Commit-Queue: Nicolas Dossou-Gbété <dgn@chromium.org>
Reviewed-by: Nicolas Dossou-Gbété <dgn@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1281702}