Previously, the chruby segment looks like this for standard and
non-standard ruby implementations respectively:
```
Ruby ruby 3.1.2
Ruby truffleruby 3.0.3
```
While displaying the RUBY_ENGINE is helpful for non-standard
implementations, showing it for "ruby" results in "Ruby ruby" which
feels redundant.
This commit adds a new configuration option to disable showing the
RUBY_ENGINE when it is "ruby". Other values for RUBY_ENGINE will always
display as before:
```
Ruby 3.1.2
Ruby truffleruby 3.0.3
```
This also makes the formatting more similar to the asdf segment:
```
Ruby 3.1.2
Ruby truffleruby-22.3.0
```
