Allow to add to Alchemy's importmap from Rails application

[tvdeyen]

What is this pull request for?

Rails applications are technically engines, but not really. For example the engine_name is the config/application.rb modularized class name. Which makes it not nice for this interface from an app developers perspective.

Let's make the interface more explicit by using a options hash with readable keys.

Example

Rails.application.config.before_initialize do
  Alchemy.admin_importmaps.add({
    importmap_path: Rails.application.root.join("config/alchemy/importmap.rb"),
    source_paths: [
      Rails.application.root.join("app/javascript/components/product_select.js")
    ],
    name: "product_select"
  })
end

Notable changes

Previously introduced Alchemy.engine_importmaps gets renamed into Alchemy.admin_importmaps

Checklist

• I have followed Pull Request guidelines
• I have added a detailed description into each commit message
• I have added tests to cover this change

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.95%. Comparing base (a1e0391) to head (4e6f189).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2884      +/-   ##
==========================================
+ Coverage   95.94%   95.95%   +0.01%     
==========================================
  Files         230      230              
  Lines        6260     6258       -2     
==========================================
- Hits         6006     6005       -1     
+ Misses        254      253       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.