Move task manager out of x-pack

[mikecote]

There are several requests to leverage task manager outside of x-pack.

In @tsullivan's case, "the Reporting plugin in the long term. Currently, OSS applications interact with Reporting but are not aware of doing so."

In @lizozom case (#92802), "_async_search is available with the Free license since 7.11. This means we can unify the data.search plugin and simplify the code." which depends on task manager.

I believe there might have been a use case at some point for telemetry (cc @elastic/kibana-core) since telemetry collection is coded outside of x-pack.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[mshustov]

I believe there might have been a use case at some point for telemetry

Another use-case that we found earlier is Notification Center #90297

[Bamieh]

for telemetry we used to have an x-pack plugin called oss_telemetry just for registering tasks for oss plugins in x-pack. This is no longer the case although not having a task manager is a limitation devs face occasionally when trying to collect data to send it through telemetry.