Document the contexts we apply to workers

What does this MR do?

This MR needs to explain how to provide context to jobs that would be scheduled without or incorrect context. Mainly Cron jobs and jobs scheduled in batch from those cron jobs.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers