feat: Add execution_state to each test

[mull]

For some reason this was removed.

To show the results for a test run we need to know:

• How many tests were scheduled
• Which of them are finished

This PR adds a column test_results.execution_state that can either be pending | completed | aborted (it is not related to the outcome of the test, only the execution.)

If a worker for a test fails this is picked up and written to Postgres.

This PR creates another issue: the result page crashes if a test fails (its execution_state is set to 'aborted'.) There is already a ticket to deal with this. If a test crashed previously the result was simply a never-ending loading page.

Since we don't have a migration system this is the DDL statement for the cluster:

CREATE TYPE execution_states AS ENUM ('pending', 'aborted', 'completed');

ALTER TABLE test_results 
  ADD COLUMN execution_status execution_states NOT NULL DEFAULT 'pending';

UPDATE test_results SET execution_status='completed';