feature request: show exit status on `cmd_button`

[lizzthabet]

buttons have the ability to replace lots of local_resources that are used to manually trigger one-off scripts. the drawback to replacing local resources with buttons is that it isn't as easy to see if a script fails or exits with an error code. with a local resource, you can see a pending, healthy, and error status.

maybe this gets into tricky territory if i want buttons to have the same state as resources, but i think it would be helpful to see at least a visual indication in the tilt dashboard that a button command has failed.

(for reference, this feature request came out of my work on !4964.)

cc: @landism @milas