Resolve "Don't create a to-do when I assign a MR or issue to myself"

What does this MR do and why?

Makes sure that to-dos are not created, when:

• user assigns themselves to work item or MR
• user assigns themselves as reviewer
• user re-requests review from themselves

Makes sure that to-do is still created, if an agent is acting for the user.

References

#340655

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable feature flag Feature.enable(:skip_todos_for_self_assignment)
2. Assign an work item or MR to yourself or add yourself as reviewer => No to-do should be created
3. Have agent do the same => to-do should be created

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #340655