Allow inviting to roles

[techsmyth]

Description

As a space admin I want to be able to invite people into particular roles in the community

Acceptance criteria

• [ ] Invitation entity extended to allow "additionalRoles" field, holding one or more roles
• [ ] Mutations for inviting extended to have this field optionally specified
• [ ] Additional roles are only assigned in the actual space being invited for, not in parent spaces (would be security gap if allowed this)

Additional Context