lifting logs to workflows whenever possible

Current situation

Execution logs are available in ExecutionResult and ExecutionError events, but other logs are not available.

It makes investigating problems not as easy as it could be.

Desired outcome

A way to get workflow-relevant logs via the observer.

Analysis

At least on the core side, most logs are produced in a context where the workflow is known.

Solution

Extend the Notification event to expose logs, and publish those events when producing log entries.

For non-workflow-related logs, we should create an Event event, similar in purpose to the Notification event, except it only relates to non-workflow-related things.

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Epic : https://project.squashtest.org/browse/SQMAP-928 Simplifier l'exploitation des logs de l'Orchestrateur
This has been promised to one client for Q1 2022 (See epic for more information.)