Implement pac connection share from #481, and a way to set connection references

[BrainSlugs83]

Just as the title says, please implement connection sharing as proposed in #481, as being able to create a connection is kind of pointless if you can't actually see it in the UI or share it with anyone.

It would be good if we could specify the id of the connection and then the upn or account of the identity to share it with.

e.g.:
pac connection share --connection-id pac-dv-00000000-0000-0000-0000-000000000000 --user 00000000-0000-0000-0000-000000000000
pac connection share --connection-id pac-dv-00000000-0000-0000-0000-000000000000 --user [email protected]

Would also be good if there was a way to set connection references to a specific connection.

e.g.:
pac connection set-reference --connection-reference-id prefix_sharedcommondataserviceforapps_d1234 --connection-id pac-dv-00000000-0000-0000-0000-000000000000