Dashboard loading state UX improvements

[RobertJoonas]

Changes

• Enable the fade-in animation when switching between IndexBreakdown tabs (e.g. Sources -> Channels) -- done by passing a key={selectedTabKey} to the IndexBreakdown components
  • Note: the animation does not trigger when changing dashboard state to something that has already been visited (i.e. the results are cached)
• WorldMap component improvements
  • initital state (data is fetching) -- render loading spinner instead of blank world map without colors
  • wrap with LazyLoader like any other IndexBreakdown (fetches data only after scrolled into view)
  • add fade-in animation when transitioning from loading -> data (or showing cached results after tab change) -- basically do the same as IndexBreakdowns
  • code organization: separate SVG rendering into a new component (world-map-svg.tsx) that assumes the presence of data

Tests

• This PR does not require tests

Changelog

• This PR does not make a user-facing change

Documentation

• This change does not need a documentation update

Dark mode

• The UI has been tested both in dark and light mode

[github-actions]

Preview environment👷🏼‍♀️🏗️
PR-6480