Expose an operation to remove a node from the cluster

[cole-miller]

We've had a request from the Juju team to add an API in go-dqlite for removing a node from the cluster configuration (as opposed to just demoting it, which automatic role management should handle if the node has become inactive). We already have this operation in the dqlite wire protocol, so it's just a matter of finding the appropriate place to add it in go-dqlite and making sure it doesn't interact badly with anything else.

[freeekanayaka]

Should be:

https://pkg.go.dev/github.com/canonical/go-dqlite@v1.11.9/client#Client.Remove

and possibly:

https://pkg.go.dev/github.com/canonical/go-dqlite@v1.11.9/app#App.Leader

to automatically get a Client object connected to the cluster leader.

[cole-miller]

Good point! I've passed that along.