Trigger Group SAML Group Sync on sign-in

What does this MR do?

Related to #267020 (closed)

On sign-in with Group SAML, when :saml_group_links feature is enabled, and the :group_saml_group_sync feature is available in the license, a GroupSamlGroupSyncWorker job is enqueued to add/remove users from groups according to groups sent from the SAML response.

This job is triggered both for new users on first sign-in and existing users on subsequent sign-ins.

This MR does not contain a changelog or documentation because the feature is still behind a disabled feature flag. !47445 (merged) includes documentation and default-enables the feature flag, and also contains a changelog entry.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
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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
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Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
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