raft: add single_node InteractionEnv test case
raft: add single_node InteractionEnv test case

Show-cases the current behavior and changes made in future commits for [^1].

The test demonstrates that a single-voter raft instance will emit an
entry as committed while it still needs to be appended to the log.

[^1]: https://github.com/etcd-io/etcd/issues/14370

Signed-off-by: Tobias Grieger <2f4c93e02da5d1f108ee22ef1e8115acadb15fa2@gmail.com>

ajityagaty/etcd,ajityagaty/etcd,etcd-io/etcd,ajityagaty/etcd,etcd-io/etcd,etcd-io/etcd