[ResponseOps] determine how to externally configure Kibana to use mget task claimer

[pmuellr]

In PR #171677, we added the ability to "pick" the task claimer to use, based on traditional Kibana config, of the value xpack.task_manager.claim_strategy. While this is functional, it may not be exactly how we want this to work.

Context:

• is this something we want users to be able to change?
• should we prefix it with internal or dangerouslySet or such?
• since we want this primarily for serverless to start with, is there some other mechanism we could use to configure it?
  • for instance, we could "sense" if we're running in serverless and enable it that way, which would also (maybe) make it harder to test ...

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)

[mikecote]

I think xpack.task_manager.claim_strategy is fine with an mget or unsafe_mget value as you have in the PR. We can leave it undocumented and once we move away from default we can either remove the config or leave it in place and ignore it.

[mikecote]

Closing because xpack.task_manager.claim_strategy should be a sufficient way for now. Once we remove default, we can either remove this setting or bypass it with mget.