Update to latest version of Pulsar `4.x`

Need to decide which version of Pulsar that Spring Pulsar 2.0.x should use.
The current version of Pulsar is `4.0.5`. 
The next minor release is `4.1.0` which seems like it may not be ready in time. 

- [ ] Reach out to Pulsar folks and get a feel on when `4.1.0` is expected
- [ ] If ready in time, go w/ `4.1.0`. If not ready in time, bump to latest patch of `4.0.x`.