chore: add ability to configure TUI via turbo.json (#7755)
### Description
Add `experimentalUI` to `turbo.json` that is equivalent to setting
`TURBO_EXPERIMENTAL_UI`
Docs update will be in separate PR to be merged on release.
### Testing Instructions
Verify that TUI is used in following scenarios:
- `TURBO_EXPERIMENTAL_UI=true turbo build`
- Add `"experimentalUI": true` to `turbo.json`
Closes TURBO-2652
