Redact or hide issue email participants based on member role

Release notes

https://docs.gitlab.com/ee/user/project/service_desk.html#privacy-considerations

Before rolling out issue_email_participants we need a to redact or hide user emails of users that are not members of the project.

At the current state when adding an email participant with /invite test@email.com in a public project the email is disclosed in a warning below the comment box to any user of the instance.

There is a solution suggested at #339777[A_Header_-_Workflow_driven_creation.png] (comment 1176556540) that could be used. It is about redacting parts of email participants depending on the user role within the project.

Also see duplicate Redact Service Desk email address when viewed b... (#353544 - closed)

Also see duplicate Not possible to hide requester's e-mail when ma... (#12243 - closed)