[feature] Dashboard builder v2

[williaster]

Creating an issue to track progress of Dashboard Builder v2 and align on intended functionality.

Functionality

V0 definition

• the UX of dashboard building will be significantly improved as it can all be done within the dashboard page
• the following components will be available for dashboard composition
  • charts (exists)
  • Markdown (exists)
  • Rows, Columns
  • Headers
  • Tabs
  • Dividers
  • Spacers

• Async dashboard content requests are more performant
  • sharded against multiple domains for higher-bandwidth loading
• Users can define color group mapping easily

V1+ definition

• scoped filters and group bys
• thumbnail previews of charts in builder
• comment threads

Feature Deprecation

It's important to note that certain dashboard features will be deprecated with these changes

• Markdown “Slices” will no longer be available in the Explore view (but available in Dashboard)
• Custom CSS will no longer be available
• Certain dashboard layouts may no longer be supported (there are some edge cases that we are still working through) and there may be some layouts that break during migration

[williaster]

closed by #4528