Improve the behaviour of clicking "view in new version" button when new version doesn't have the same guide path

When viewing an old guide you always see a link to "view the current guide in latest version" at the top of the page:

If you click the link in a guide that has been deleted in the latest verison (i.e. the path is not valid any more) then you will see a 404 page error:

Interestingly, because this is not a 404 path and just the error template clicking back in the browser does not get you out of this situation 🙈 you need to instead refresh.

### Steps to recreate

- start the appliation locally
- visit http://localhost:4200/v1.2.0/getting-started/editing
- click the `VIEW v1.3.0` button
- 💥

### Todo

- [ ] make this experience "better" for people
- There is a full discussion of this problem [in an issue on guides-source](https://github.com/ember-learn/guides-source/issues/495)
- this issue probably reuquires some experimentation and discussion with the @ember-learn/learning-core-team
- [ ] improve the experience of using the back button when this situation happens
- this could be a guidemaker concern so might need to be done "upstream"
- ember used to have the concept of eager transitions but it seems to have been removed in 1.12 🙈 (makes me feel old). Fixing this will require research and discussion
- If this is too hard for now we can pull it out into a separate issue so it doesn't block the work 👍

Reproduce the problem at /v1.2.0/getting-started/editing and click the VIEW v1.3.0 button. Read the linked guides-source issue #495 and investigate whether the fallback belongs in this template or upstream in Guidemaker. The issue needs an agreed solution for missing guide paths and the browser back-button behavior before implementation can be considered done.

Written by the indexing model from the issue text.