feat: [AppsChat] Add Carousel widget (#8664)

* feat: Add `Carousel` widget
feat: Add `OverflowMenu` widget
feat: Add `NestedWidget`
feat: Add the field `TextParagraph.max_lines`
feat: Add `Validation` and the field `TextInput.validation`
feat: Add `Button.Type` and field `Button.type`
feat: Add `ChipList`,`Chip` and field `Widgets.chip_list`
feat: Add the field `TextParagraph.TextSyntax`
feat: Add the field `DecoratedText.start_icon_vertical_alignment`
fix!: An existing field `start_icon_uri` is moved in to oneof in message `.google.apps.card.v1.SelectionInput`
fix!: Changed proto3 optional flag of an existing field `multi_select_max_selected_items` in message `.google.apps.card.v1.SelectionInput`
docs: change `Workspace Add-ons` to `Workspace add-ons`
docs: improve comments

PiperOrigin-RevId: 820227260

Source-Link: googleapis/googleapis@fef7009

Source-Link: googleapis/googleapis-gen@1d97deb
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Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]