Show remaining epic issue count and total weight in epic boards

Challenge

This is based on my comment in the MVC1 for Epic boards - #324677 (comment 558440784)

While using the early access to Epic Boards one thing we have found that would be really useful is to see the number of remaining open issues and the total weight of those issues. The issues board does something similar and show their weight.

Proposal

Figma doc.

• Epic card: Add issue count and total weight to each epic card with a corresponding tooltip.
  • I'd envision the tooltip of the count being consistent with the tooltip in the epics, something like:

• List header: (This or next iteration) Add a progress roll-up to each column list header with a corresponding tooltip.
  • Use the progress icon
  • The tooltip for column progress could be similar to roadmaps, like: