Document both button shapes on the survey.button.clicked webhook

[mamuh]

• Document both legal shapes of data.button on survey.button.clicked, since a Microsurvey click now resolves a Question's answer Button as well as a page Button — the page shape was the only one published
• Name question_id as the discriminator, and warn against branching on tour_action, which an answer Button does not reliably carry and which returns undefined for a Question answer
• Add a Question Button property table (question_id, order, enabled, and score_type with its detractor / passive / promoter buckets on nps) so a subscriber can read a scale answer without guessing
• Point the survey.button.clicked topic row and the shared button-click example at the new section, following the page's existing pattern for a topic whose object shape differs

🤖 Chameleon dev for CORE-314