✨ [Web Story] Update the share text for share flow

[ychsieh]

Add more information in the share text. This is for users to understand more about the story shared on various platforms.

[amp-owners-bot[bot]]

Hey @gmajoulet, @newmuis! These files were changed:

extensions/amp-story/1.0/_locales/en.json
extensions/amp-story/1.0/amp-story-share-menu.js
extensions/amp-story/1.0/amp-story-share.js
extensions/amp-story/1.0/amp-story-store-service.js
extensions/amp-story/1.0/amp-story.js
src/service/localization/strings.js

[stale[bot]]

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