Ask branch for edgedb instance link if >=5.0

[quinchs]

Fixes #1269

Remarks I made the instance_main entry as tokio::main to fix some async issues later in the call chain, seems to have no outstanding negative effects.

[quinchs]

The reason we don't ask database/branch always is pre-5.0 never asked for the default database iirc. I don't mind changing this behavior.

This would allow the server to provide its default for the branch. We can then read it with another query, so that it can be written into the config.

I think this is good.

[quinchs]

Blocked on the changes to the edgedb-rust binding regarding branch connection

[aljazerzen]

This is now failing only because we are not respecting --non-interactive.