Fixes #37792 - Safe mode and bootdisk_* template helpers

[stejskalleos]

Using :extend_template_helpers instead of :allowed_template_helpers
fix the issue when rendering bootdisk_* template helpers in the Safe mode.

For steps to reproduce, see https://projects.theforeman.org/issues/37792

[nofaralfasi]

Failing tests are related.

[stejskalleos]

Moving to draft, current changes breaks the full-host iso generation

[stejskalleos]

@nofaralfasi ready for review

tested subnet, host image and full host images and all generated correctly

[nofaralfasi]

This fix resolved the issue for me, but I'm unclear about why this change was necessary. @stejskalleos, could you please explain the reason for these changes? I’m assuming it was working previously, so what led to this problem?

[stejskalleos]

@nofaralfasi I believe the reason is the recent move to Zeitwerk and its way of loading modules and classes.

With the original approach, the ForemanBootdisk::Scope::Module wasn't loaded before the Foreman's render method tried to access methods from it, causing the no method error.

[nofaralfasi]

I must admit that I still don’t fully understand some of these changes, such as the necessity of keeping the ForemanBootdisk::Scope::Bootdisk class. However, since this resolves the issue, I don't want to hold up the merge.

[stejskalleos]

Zeitwerk follows a strict file structure-to-module/class mapping.

For example, having this code:

module ForemanBootdisk
  module Templates
    module Scope
      # do something
    end
  end
end

It requires you to have the following files:

foreman_bootdisk.rb
foreman_bootdisk/templates.rb
foreman_bootdisk/templates/scope.rb

Zeitwerk maps namespaces (modules or classes) to the corresponding file paths. When a constant like ForemanBootdisk::Templates::Scope is referenced for the first time, Zeitwerk looks for the file templates/scope.rb within the foreman_bootdisk directory. If the modules are defined within the same file, Zeitwerk won't be able to autoload ForemanBootdisk::Templates::Scope correctly.

cc @ofedoren please feel free to correct me if I'm wrong.