Implement a more fine-grained sharing mechanism

[danilhendrasr]

One of the feature this project's trying to achieve is easy sharing of workspaces, I take Google Docs and Miro as an example too. But at the moment it only has a very minimal implementation of workspace sharing, which is every public workspace is accessible to anyone who has the link. I think implementing a more fine-grained sharing mechanism will get the feature closer to what I envisioned.

For example, users can do:

• Share workspace to specific users (by email)
• Share workspace to everyone who has the link

Having permission per invited user is also good, but I'm not sure if I can complete it in time. So it's probably better
to limit this issue to just 2 items above.