[dagit] Add "Download debug file" to Run page
Modify the upper right of the Run page to make the button a menu with two items:
- View tags and configuration (opens a dialog, just as before)
- Download debug file (same as on the Runs list view)
Test Plan: View a Run, verify that the menu behaves correctly for both items.
Reviewers: bengotow, prha, alangenfeld
Reviewed By: bengotow
Differential Revision: https://dagster.phacility.com/D8651