Add "What's New" Section

[yuriy-fix]

Description:
Add a "What's New" section in the documentation menu to display newly added features, components, and articles for the selected version.

Details:

• Filter by Version: Show updates relevant to the selected version using version-specific tags.
• Content Display:
  • New Components/Articles: Links directly to the new documentation page.
  • New Features in Existing Articles: Displays the article name with a badge (e.g., New Feature) and links to the specific heading/section where the feature is described.
• Badge Options: Use New Feature, Experimental, or similar for clarity.

Benefits:

• Makes it easier for users to discover new features and components.
• Promotes visibility of experimental features (things under feature flags).

[jouni]

What’s the plan, how often are the items in this section updated? Who decided what is added and when when is an item removed (when does it stop being "new")?

[yuriy-fix]

We hopefully could make it automatically check the version tags used within the articles to decide on inclusion of the feature. since:com.vaadin: the selected version.