[Admin] Introduce role creation

[MadelineCollier]

This is basically just a repost of this PR: #5826 with a new base branch.

This PR is for #5823. The update/edit functionality will follow in a second PR to keep things small and easy to review. Currently this is just the index, new, create, and delete methods.

This PR creates a new role management page in the new admin interface, following the existing pattern used for tax categories and refund reasons.

The form is rendered via a modal dialog on the roles list by leveraging Turbo frames. Successful creation leads to a turbo stream page refresh, which updates the existing list preserving the query params and the scroll position, for a consistent UX.

The attached video shows the functionality visually:

New tab nesting, scoping, and role creation:

Screen.Recording.2024-08-14.at.7.05.11.PM.mov

Deletion:

Screen.Recording.2024-08-14.at.7.08.38.PM.mov

Additional Questions

This is the first piece for the new [Admin][Settings] Introduce role creation and modification capability ticket.

Example designs:

Spree::Role currently lacks:

• Types
• Descriptions
• Any validation on "Name" except that it be unique (it is still allowed to be blank).

I am assuming that to support the example designs, I will be adding those attributes to the Spree::Role model in a future PR, but I am unsure whether that should go in solidus_admin or whether that should be added to core.

Additionally, the example designs seem to differentiate between "custom" and "standard" roles. Will we be creating new stock roles with default permissions sets and adding them to core/db/default/spree/roles.rb? If so, what will those default roles and permissions be?

Summary

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.12%. Comparing base (b766363) to head (1fbe6d5).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5831      +/-   ##
==========================================
+ Coverage   89.08%   89.12%   +0.04%     
==========================================
  Files         739      743       +4     
  Lines       17246    17317      +71     
==========================================
+ Hits        15363    15434      +71     
  Misses       1883     1883              

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