Documentation of v4.x is mentioning features of 5.x

The documentation of Bolt 4.x seems to be mentioning features that are actually not implemented in this branch, but are in 5.0.
It might be worth taking some time to check it, because the doc should reflect the reality, and it is both time-consuming and frustrating to try using a feature that is documented, seeing it does not work, double-checking we didn't make any typo, and finally reading the source code in `bolt/core` just to find out it is actually not implemented in the version you are using.

Just got the issue while reading [the Viewless part](https://docs.boltcms.io/5.0/howto/resource-contenttype#viewless) of the Content-Types page, that is mentioning a `viewless-listing` option, which is actually implemented only from 5.0, as you can see in this diff:

https://github.com/bolt/core/compare/4.2.5...5.0.0#diff-800486d2d7822cc4f26e4df7fd368566b7b43a92562cfba0a9b5434fc5cd987aR51-R53