[Error Handling] - Backend - Stopping a Test Run

[xoscar]

We need a way for the BE to stop in-progress test runs

Acceptance Criteria

AC1
As a client triggering a test run
I should be able to trigger an endpoint to stop the test run
The polling service should halt the execution,
The test run state should be switched to STOPPED
The partial trace (if any) should be stored
And the test specs execution should be skipped