SCAL-332735 Add TSE customization for Spotter on Liveboard

[ramjith-thoughtspot]

SDK counterpart of scaligent #67191, which lifted the hard isEmbedded block on Spotter chat and put it behind the standard embed action contract.

Jira: SCAL-332735

Changes

• Action.SpotterOnLiveboard ('spotterOnLiveboard') — new action so hosts can control the Spotter chat entry point on an embedded Liveboard: hiddenActions removes the panel and header button, disabledActions greys the button and surfaces the host's disabledActionReason. Matches the enum value added to blink's embed-util in #67191.
• StarterPromptsConfig.liveboard?: StarterPromptQuestion[] — starter-prompt customization for the Spotter chat panel on a Liveboard, alongside the existing quick/research/previewData categories. Delivered through the existing starterPrompts APP_INIT payload (buildStarterPromptsAppInitData), so no new plumbing.
• SpotterChatViewConfig.openSpotterOnLiveboardByDefault?: boolean — opens the Spotter chat panel on the Liveboard by default. Passed as a URL query param (Param.OpenSpotterOnLiveboardByDefault) by both LiveboardEmbed and AppEmbed, following the same pattern as the other spotterChatConfig sub-flags.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@thoughtspot/visual-embed-sdk@628

commit: a8b9000