[Enhancement] Kibana centralized push notification framework to replace a polling mechanism for Kibana background jobs.

[YulNaumenko]

Describe the problem to solve:
Set of the Kibana UIs, which are using background tasks for a long running jobs, are using polling mechanism (in some cases also an additional status storage) to identify if the job was completed and with what status to notify the user: Security Attack Discovery, SIEM Migrations, ML jobs, Reporting.
Example of the Reporting architecture, created by @tsullivan:

Describe the feature:
The feature request is about the centralized Kibana push notification framework, which will use WebAPI Push API or the other modern capabilities to push notifications to the client. This could simplify the complexity and effort needed to support user notifications with the polling mechanism.

[elasticmachine]

Pinging @elastic/appex-sharedux (Team:SharedUX)

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[tsullivan]

@elastic/kibana-core this would be a very useful and significant architectural improvement. Is something like this on your radar?

[TinaHeiligers]

Core investigated something very similar a few years back with the centralized notification service that was closed as not planned.

We could revisit the idea and possibly reuse some of the original work if the requirements overlap and if the initiative would benefit solutions.