Expose NewNodeConsoleNote as Beta.class so LogStorage implementations can interact with it

[dwnusbaum]

NewNodeConsoleNote is special in that custom Pipeline log visualizers that are not based on the Jenkins ConsoleNote-related APIs likely still want to display the associated lines differently or suppress them entirely (see additional discussion in #371) rather than just ignoring the markup and showing the raw text content.

For my use case, I can get away with only checking a hard-coded class name against ConsoleNote.readFrom(...).getClass().getName() in production code (in fact I can actually reference the class literal due to jenkinsci/lib-access-modifier#166), but I would like to mark this class as @Restricted(Beta.class) to make it clearer that API changes should be considered carefully and that incompatible changes should probably be moved to a different class. I would also like to be able to use NewNodeConsoleNote.print in tests without having to worry that the API is going to be modified unnecessarily, and to be able to reference the class literal in production code if jenkinsci/lib-access-modifier#166 is fixed.

Testing done

### Submitter checklist
- [x] Make sure you are opening from a **topic/feature/bugfix branch** (right side) and not your main branch!
- [x] Ensure that the pull request title represents the desired changelog entry
- [x] Please describe what you did
- [ ] Link to relevant issues in GitHub or Jira
- [x] Link to relevant pull requests, esp. upstream and downstream changes
- [ ] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[jglick]

Seems reasonable; the bar is low enough for Beta and I do not know of any particular plans to rename or delete this class (there is not much signature inside it to change).