Fix display of promote to group label

What does this MR do?

Fix display of promote to group label

Since label presenter is used in label index view, label class check doesn't work as expected because the class is now LabelPresenter.

Also label.subject doesn't work as expected now because Label's model subject method is shadowed by Gitlab's presenter's method which uses subject for referencing the original object.

Instead we use a presenter's method for both checks now.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/62200

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
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Performance 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

Security

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