feat: support search summarization
feat: support structural search features
feat: support image search
feat: added query expansion details in search response
feat: support bring your own embedding feature
feat: support tail suggestions in completion API
feat: allow uri in user events
chore: deprecate SnippetSpec max_snippet_count and reference_only
docs: keep the API doc up-to-date with recent changes
PiperOrigin-RevId: 561158238
