fix: base resource overriding

[Paul-Bob]

Description

Fixes #3073

Base resource extension was not possible with the Avo::BaseResource on lib/avo/base_resource.rb path.

This PR moves lib/avo/base_resource.rb to app/avo/base_resource.rb and adds the engine's directory app/avo to autoloaders.

ActiveSupport::Dependencies.autoload_paths.delete(directory_path) is only necessary for Rails lower than 7.1. For more context check fxn/zeitwerk#250 (comment)

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
  • Docs are already according to this configuration
• I have added tests that prove my fix is effective or that my feature works

[codeclimate]

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[adrianthedev]

Nice!

[github-actions]

This PR has been merged into main. The functionality will be available in the next release.

Please check the release guide for more information.