SubmittingPatches: extend release-notes experiment to topic names

SubmittingPatches: extend release-notes experiment to topic names

In d255105c99 (SubmittingPatches: release-notes entry experiment,
2024-03-25), we began an experiment to have contributors suggest a topic
description to appear in our RelNotes and "What's cooking?" reports.
Extend that experiment to also welcome suggested topic branch names in
addition to descriptions.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>