[Logs UI] Add ML module with a common log categorization job

[weltenwort]

Summary

Following the investigation in #46610 the categorization can probably be handled using a single ML job.

Job results

The following result data structures could be attributed to a partition:

• the anomaly record
• the model_plot with the actual count per bucket and partition

A few result data structures would be shared between the partitions:

• the bucket
• the category with its examples

Acceptance criteria

• A new ML module logs_ui_entry_categorization with one job and one datafeed exists.
• The job is a categorization job with...
  • a categorization_field_name set to message.
  • a count detector with the by_field_name set to mlcategory and partition_field_name set to event.dataset.
  • a bucket_span of 15 minutes.
  • the model plot enabled.
• The datafeed for the job...
  • filters the documents for the existence of a message field.

[elasticmachine]

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