[Logs UI] Load log entry examples using async searches

[weltenwort]

Summary

As part of the make-it-slow effort (and thereby indirectly searchable snapshots and runtime fields) we want to use Elasticsearch's async search to execute potentially expensive queries. The queries to load the log entry examples in the "Anomalies" and "Categories" tabs certainly qualify as such.

related to #86439

Acceptance criteria

• A search strategy for loading intervals of log stream entries exists.
• The log entry examples on the "Anomalies" tab are loaded using the corresponding search strategy.
• The log entry examples on the "Categories" tab are loaded using the corresponding search strategy.
• The requests are cancelled when newer requests are issued.
• The requests can be explicitly cancelled and retried by the user.
• The previous HTTP routes are not present anymore if no other usage remains.

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[jasonrhodes]

Refinement update: ML tabs are not using async search.