vdk-jupyter: introduce a polling mechanism in the backend that would execute tasks in the background and track their status

[yonitoo]

What is the feature request? What problem does it solve?
The VDK JupyterLab extension encounters the following problem: it receives a 504 Gateway Time-out error while waiting for a long process to conclude. This error likely comes from an intermediate proxy or the server configuration due to prolonged inactivity.

Suggested solution
The idea is to introduce a new class TaskRunner that would provide a polling mechanism. It would have an interface similar to this:

• start_task(id, task_handler) -> T/F (or something else); task_handler is a lambda function that would execute what the post methods of the current derived APIHandler classes do
• get_status(id) -> complex output dict/structure/class that would contain at least the following keys: "status", "message" and "error". It would be used to check the status of the currently running task and if the task has finished - proper message and error.

We would check the status of the ongoing task every x seconds or following some other pattern, having some threshold number of status checks. After the last one, if the task is still ongoing, we will return some kind of error to the user.

Additional context
It is a follow-up of the solution provided in #2789.