[DOCS] Confusing description and broken link for config.action_view.erb_trim_mode

[sobstel]

Gives the trim mode to be used by ERB. It defaults to '-', which turns on trimming of tail spaces and newline when using <%= -%> or <%= =%>. See the Erubis documentation for more information.

The only possible option for config.action_view.erb_trim_mode is -, which - if set - enables trim mode (https://github.com/rails/rails/blob/47300002db11d67d7b35103f5c429dad7dacdacd/actionview/lib/action_view/template/handlers/erb.rb#L81) and it's not used anywhere else. Any other option is not possible.

Previous try to fix it https://github.com/rails/rails/pull/50157 was rejected, but this actually correcty describes current behaviour.

Also, Erubis documentation links is broken. It constantly gives Error: Server Error. I'm not sure if this is needed at all considering the only possible option is "-" .