[WEB-2500] feat: Product updates modal (What's new in Plane)

[prateekshourya29]

Media

Issue link - WEB-2500

Summary by CodeRabbit

• New Features

  • Introduced a new endpoint for accessing instance changelogs.
  • Added a new environment variable INSTANCE_CHANGELOG_URL for configuration.
  • Implemented a ProductUpdatesHeader component displaying the current version and updates.
  • Created a ProductUpdatesModal for viewing product updates in a modal format.
  • Added a ProductUpdatesFooter with links to documentation and support.

• Bug Fixes

  • Removed outdated components related to product updates to streamline the user interface.

• Documentation

  • Updated components to improve accessibility and user experience.