Hide internal comments from all non-project/group members

Issue

Internal comments are currently visible to epic/issue authors, even if they're not a member of the project/group. This is confusing and slightly misleading as the term internal makes it seem as if the comments are visible only to internal members.

Relevant slack thread: https://gitlab.slack.com/archives/C03MSG8B7/p1665414459963309

Proposal

Hide internal comments from all non-project/group members