Allow to disable changing additional e-mail addresses

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Is your feature request related to a problem? Please describe.
https://github.com/nextcloud/server/commit/eb98e99530aaf430cd8759b1ade94e2686a06920 introduced allow_user_to_change_email to disallow user modify their primary e-mail address but user still may modify their additional e-mail addresses when allow_user_to_change_email is disabled which may be undesirable (i.e. when user's data is populated from LDAP).

Describe the solution you'd like
Please consider disabling also additional e-mail addresses changing with the same parameter or with separate parameter i.e. allow_to_change_additional_emails as proposed in https://github.com/nextcloud/server/pull/33795

Review commit eb98e99530aaf430cd8759b1ade94e2686a06920 and pull request #33795, then trace how allow_user_to_change_email controls primary address changes. Determine whether additional addresses should follow that setting or use a separate parameter, and verify that the selected behavior prevents unwanted changes when directory data is authoritative.