fix outdated settings related to default layout preview

[lucasgeron]

What are you trying to accomplish?

• Fix wrong docs related to setting up a default layout for preview components.
• Fix some lint offenses.

What approach did you choose and why?

• Explore the configuration structure with Rails.application.config.view_component and notice that the documentation configuration is not working properly.

Before:

# with config.view_component.default_preview_layout = "component_preview"
{:generate=>{...},
 :previews=>
  {:controller=>"ViewComponentsController",
   :route=>"/rails/view_components",
   :enabled=>true,
   :default_layout=>nil, # value as nil
   :paths=>[...]},
 :instrumentation_enabled=>false}

After:

# with config.view_component.previews.default_layout = "Component_preview"
{:generate=>{...},
:previews=>
 {:controller=>"ViewComponentsController",
  :route=>"/rails/view_components",
  :enabled=>true,
  :default_layout=>"component_preview", # correct value
  :paths=>[...]},
:instrumentation_enabled=>false}

Anything you want to highlight for special attention from reviewers?

• Is required to review if the current config.view_component.default_preview_layout is still in use or should it be removed.