Add changelog agent workflow (#61097)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Sarah Schneider <sarahs@github.com>
Co-authored-by: Sarah Schneider <sarahs@users.noreply.github.com>

Author: 4 people