Sign in from untrusted IP address user_access_locked audit event

What does this MR do and why?

Resolves https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/244?work_item_iid=415 as part of https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/244.

Update the message of the logged user_access_locked audit event to include a reason ("User access locked - sign in from untrusted IP address") when a user's access is locked after signing in from an untrusted IP address.

MR acceptance checklist

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