Delete user from rotation if user is deleted [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

When a user is deleted from the GitLab instance we should handle the removal of the user from oncall rotations in a predictable way.

This change runs the IncidentManagement::OncallRotations::RemoveParticipantService as the user is being deleted to ensure that:

• Any current shift the user is part of is ended
• The shifts are recalculated moving forward
• An email is sent to the owners & participants informing them the user has been removed from the rotation.

To read more about the IncidentManagement::OncallRotations::RemoveParticipantService see the MR which introduced it !59427 (merged).

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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  • I have not included a changelog entry because _____.
• Documentation (if required)
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• 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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #323631 (closed)