Improve asynchronous tasks error handling and reporting

[davelopez]

Closes #19419

When a Celery task failed, there was no way of getting the error message to the user to inform them exactly what the failure was.

This PR adds a new endpoint GET /api/tasks/{task_id}/result that will return the status and the final result message. In case of failures, the result message will contain the error message.

The rest of the changes adapt the task monitoring and persistence composables in the client code to display and store the error message accordingly.

Before

After

How to test the changes?

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  • Follow the steps in workflow export wizard flow improvement #19419

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[davelopez]

Test failures unrelated