Group-level audit event for Group SAML SSO

What does this MR do?

Fixes #35710 (closed)

Create a group-level audit event when a user signs in via Group SAML. The current audit event was a user audit event and only appeared to individual users and to administrators in the instance audit events.

Screenshots

• Note that the way the audit events display is not part of this MR. This only adds the event which is then shown according to a standard for audit events. This is just an example.

Group-level audit event

Instance-level audit event

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
• 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