ENH Return PJAX responses from gridfield edit forms

[GuySartorelli]

Description

Adds a PJAX response negotiator to GridFieldDetailForm_ItemRequest so that javascript which is expecting PJAX responses will get what it's expecting.

Note there's a kitchen sink CI run linked in the main issue

Manual testing steps

1. Add silverstripe/frameworktest to a project and make sure all of the operations work as expected for companies (which are versioned) and employees (which are not versioned) in "Test ModelAdmin"
2. Add an elemental area to the Company class (yml config snippet below), add a block with an upload field (e.g silverstripe/elemental-fileblock) and make sure you can upload a file to the block and save with the page save button.

SilverStripe\FrameworkTest\Model\Company:
  extensions:
    - DNADesign\Elemental\Extensions\ElementalAreasExtension
  has_one:
    ElementalArea: 'DNADesign\Elemental\Models\ElementalArea'
  owns:
    - 'ElementalArea'
  cascade_duplicates:
    - 'ElementalArea'

Issues

• UploadField inside inline-editable element doesn't update when saving parent record in a GridFieldDetailForm silverstripe-elemental#1156

[GuySartorelli]

Note that while this is being implemented to facilitate fixing a bug, the approach is somewhat more risky in terms of chance of regressions than I feel comfortable with in a patch release - hence targeting 5 instead of 5.2.

[GuySartorelli]

Doing this here means it applies for the save and publish actions, with a relatively low chance of affecting custom actions people add.

[GuySartorelli]

I went with this approach because admin uses PJAX for the form submission and elemental expects a PJAX response in return. It doesn't make a distinction between different admin sections or different contexts for the form, nor should it.

[emteknetnz]

There's also and admin behat failure on the sink run https://github.com/creative-commoners/recipe-kitchen-sink/actions/runs/8808259049/job/24177023040 - I've tried rerunning once though the same error has appeared so it's probably legit

[emteknetnz]

Tested locally, works good. CI failures are expected