Selectable permissions for new members

[DLBPointon]

Is your feature request related to a problem? Please describe

I am running GitPod as an educational tool, and requesting new members join means they join the organisation as a Member which is undesirable as it means they can see a lot more than I want them to. This should be a drop-down so I can default this behaviour to Collaborator or perhaps a set of custom permissions (although that doesn't matter right now).

Describe the behaviour you'd like

A selectable drop-down in the organisation's settings page to select the default permissions given to someone using the invite link.

Describe alternatives you've considered

The alternative is going through one-by-one and setting the permissions manually which isn't helpful when I'll be setting this up for >1000 people.
This would be useful even if it was part of the paid tier.

Additional context

This is so these members can join my organisation and make use of the Prebuilds without access to anything else.