Add top discovery tab and collapsible header
Summary
Add the Top tab on the discovery screen and reactors the screen to support collapsible header
closes #4071 (closed) #4053 (closed)
Steps to test
- Open discovery
- Top tab should be there and it should be the default one
- Scroll and the header should disappear
- Scroll back a little
- The header should appear again
Estimated Regression Scope
This MR only affects the discovery screen