Block a user at the group level

• Block a user at the group level.
• A group admin can block any user in the group.
• When a user is blocked from a group, they can no longer participate in the group (in all projects, including subgroups). But they can participate in other groups in the GitLab instance.
• A group admin can unblock at any time.
• There is no ability to expire the block automatically. That is out of scope.

mentioned in issue #19313 (moved)

@victorwu What happens when blocking a member from a public group? Do they lose access entirely, or just their "member privileges"? In other words: Does blocking a member have the exact same effect as deleting their membership (while being reversible), or is this even more strongly a block/ban from interacting with the group entirely?

@DouweM : The original thinking here is that we want to give moderation tools to the group level, i.e. group admin. I would think that in most cases, these would be private projects in a group anyways, so blocking them means that they couldn't do much anyways as a result of "losing their membership to the group". So I think it's okay that it's a "lighter" block in that sense. Equivalent to them not being a member of that group. Did you have any particular thoughts on this?

@victorwu I hoped it would be exactly that, because it's easier to implement, so thanks for verifying :)