[Admin] Create new Adjustment Reasons

[MadelineCollier]

Summary

This PR is for this issue but it doesn't have an issue ID yet as the issue is still in draft. The update functionality will follow in a second PR to keep things small and easy to review.

This PR migrates the creation of new adjustment reasons to 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 adjustment reasons 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:

Screen.Recording.2024-08-07.at.4.20.09.PM.mov

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[MadelineCollier]

Not sure if the spec failures I am seeing here are related to my changes, but happy to fix if they are!

Locally my new specs pass:

Example spec failure from CI just now:

[kennyadsl]

@MadelineCollier it seems like something related to Ransack, which released a new version recently. If you want to take a look, that would be great.

[MadelineCollier]

@MadelineCollier it seems like something related to Ransack, which released a new version recently. If you want to take a look, that would be great.

I have opened a separate PR to address this issue:
#5812

[codecov]

Codecov Report

Attention: Patch coverage is 97.05882% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.80%. Comparing base (b3111b2) to head (b5b0493).

Files	Patch %	Lines
...ers/solidus_admin/adjustment_reasons_controller.rb	95.83%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5811      +/-   ##
==========================================
+ Coverage   88.78%   88.80%   +0.02%     
==========================================
  Files         731      732       +1     
  Lines       17057    17088      +31     
==========================================
+ Hits        15144    15175      +31     
  Misses       1913     1913              

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