Support get tasks and hot_threads API from remote clusters

[dnhatn]

The tasks and hot_threads APIs are critical for debugging slow search or ES|QL requests. However, with CCS, we need direct access to remote clusters to retrieve tasks or hot_threads. In many cases, we don't have access to these remote clusters except for the admin. Also, if a _search or ES|QL request hits many remote clusters, we need to manually retrieve tasks and hot_threads from each cluster individually.

Should we support getting the tasks and hot_threads from remote clusters?

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[elasticsearchmachine]

Pinging @elastic/es-distributed-coordination (Team:Distributed Coordination)

[ywangd]

Tagging the @elastic/es-security team as well for awareness

[elasticsearchmachine]

Pinging @elastic/es-security (Team:Security)