fix bg tasks display logic

[peterkeppert]

@JoshuaC215 , let's finish this in your branch. after your review, I have updated 3 things here:
In task.py: Task statuses so that the "started" entry gets displayed when task is started
In streamlit_app.py:

• Logic to determine container states based on child tasks' states
• Removed "break" after encountering an "error" task state. If there is another task besides the error one which is still running, we should wait until they all complete, before declaring the container state to be "error".

[JoshuaC215]

@peterkeppert I pushed some bug fixes to your PR.

I think in your version you were trying to support multiple parallel bg tasks? But I still don't think the code worked the way you intended, since only one status container was ever open at a time. At least to me the logic and for loop seemed confusing.

If you want to make parallel bg tasks work in the UI before merging this PR, please make it so bg_task_agent.py sends multiple parallel bg tasks and test to make sure it works how you expect.

Otherwise if you're OK with this version we can merge it in and merge the branch to main.