Disable terminate button if run cannot be cancelled
The cancel_pipeline_execution mutation returns a CancelPipelineExecutionFailure if run.status is not PipelineRunStatus.STARTED.
This diff updates the UI to disable the "Terminate" button if run.status !== PipelineRunStatus.STARTED
Test Plan: Execute pipeline, wait for execution to finish/error, verify Terminate button is disabled
Reviewers: #ft, sashank
Reviewed By: #ft, sashank
Differential Revision: https://dagster.phacility.com/D1351